So what can we expect from the blockbuster launch event at the Yerba Buena Centre for the Arts in San Francisco?
As with pretty much every Apple launch since the company turned around its fortunes in 2001 with the original iPod, there has been an avalanche of speculation, leaks, rumours and hype around what Apple boss Tim Cook will unveil.
The entire world seems to think that the iPhone 5 will finally surface, but that is what we expected in October 2011, only for Apple to instead announce the iPhone 4S.
The iPhone is the most valuable product in Apple's arsenal, and the firm shifted over 35 million of the smartphones in the first quarter of 2012 alone.
Due to the feverish anticipation - and clear signs that many legacy iPhone owners are primed to upgrade - it is thought that Apple could sell more than 5m iPhone 5s in the opening weekend and 10m in the first week. And these are sales estimates for a product that hasn't even been announced!
So, here is a roundup of the latest rumours about the iPhone 5, along with other things to expect from the launch event, such as more details on iOS 6, possible fingerprint technology and a refresh to the iPod line.
Apple's invite features the number "12" denoting the date of the launch, but also tellingly has a "5" reflected underneath. The new iPhone is often referred to as the "iPhone 5" as it will be the successor to last year's iPhone 4S.
The handset is technically the sixth generation of the product, and there was some speculation that Apple would simplify the branding to just "iPhone", as it did with the third generation of the iPad. However, it seems Apple intends to stick with the numerical branding and this will be the iPhone 5.
Apple may be fooling everybody and instead launch five new devices at the event today, but for a firm known for its limited product range, that appears unlikely.
The iPhone 4S sold very well, but was met with a rather underwhelmed response when it was launched last October as it offered just an upgrade on the iPhone 4 introduced in 2010. The iPhone 5, however, is expected to be much bolder.
According to the latest leaks, the handset will be taller than its predecessor in order to accommodate a new 4-inch screen, up from the 3.5 inches in the current models.
However, it is expected to achieve this extra screen real estate whilst still being the same width as the iPhone 4S and also slightly thinner. Magic, huh?
The larger screen would give a better experience in widescreen with a 16x9 aspect ratio, as well as display more information in portrait mode, particularly with web pages and images. However, the display will be much smaller than some of the iPhone 5's competitors, including the 4.8-inch-screen Samsung Galaxy S3.
But Ian Fogg, senior principal analyst for mobile at IHS, noted: "A larger iPhone screen will be even more suited to video playback than older models if Apple adopts a widescreen 16x9 aspect ratio.
"Apple's new iPhone will again transform the market for mobile content. This time Apple will revive the market for on-demand mobile TV and video."
Apple is expected to include the high resolution Retina display that featured in the iPhone 4 and 4S, along with IPS - a technology offering improved colour contrast and viewing angles. It is expected that the screen res will be boosted to 1136x640 pixels, from 960x640 in the iPhone 4S, boasting 326 pixels per inch.
There have been reports that the thinner form factor is down to new in-cell touch technology that integrates touch sensors into the LCD, meaning it is not necessary to have a separate touchscreen layer, as in previous Apple products.
Apple's iPhone 5 screen suppliers are expected to be LG Display, Sharp Corp and Japan Display Inc.
Under the hood, the iPhone 5 may pack the same A5X dual-core processor as in the new iPad, offering zippier performance across a range of tasks, including video streaming and rich media. It will also most likely have better graphical capabilities for gaming.
Rumours of a new dock connector abound, suggesting that this is almost a dead cert. It is thought that the new iPhone will have a smaller dock than the current 30-pin port that has featured in Apple mobile devices since the third-generation iPod was released in 2003.
It was initially thought that the smaller dock would be a 19-pin version, but a French website put the cat amongst the pigeons at the weekend by publishing supposedly leaked images of a 9-pin port, featuring eight exposed pins and the metal dock acting as the ninth.
The site claimed that this new dock design, said to be the size of a micro-USB, would enable iPhone users to input the connector without needing it to up the right way, just as they do with the MagSafe dock in newer MacBooks.
Whatever the design, it is widely expected that Apple will slim down the connector to free up space in the iPhone body. Other reports claim that the headphone jack will move to the bottom of the handset, capitalising on the extra space.
However, this does mean that the iPhone 5 will not be compatible with older accessories or chargers, meaning Apple will most likely offer some kind of adaptor. The firm is also expected to announce improvements to its AirPlay system which streams content wirelessly from iOS devices to compatible entertainment systems.
A recent report stated that this will include a new 'AirPlay Direct' system of Bluetooth streaming audio, joining the already available WiFi streaming.
Another change expected to be ushered in with the new iPhone is in Apple's headphones, which have been the same in Apple iOS devices for a number of years, and not particularly liked by users.
A pair of what were claimed to be Apple's new headphones recently leaked on a Vietnamese website, revealing a major redesign to the white in-ear buds.
If the report is genuine, the new Apple headphones feature a more streamlined design and involve one piece of plastic that is said to be more comfortable in the ear. It is thought that they will become standard on Apple products after the iPhone 5 launch.
Pretty much every new generation of the iPhone has offered a better camera, and that is not expected to change with the iPhone 5.
Apple may opt to stick with the 8-megapixel rear-fitted camera with flash introduced in the 4S, albeit with some software upgrades and so on. Or it may fit an entirely new camera on the phone, potentially with a better sensor. This decision may be based on whether it feels consumers need more than 8MP, being as that is fast becoming the smartphone standard.
But one area where improvement is definitely expected is the front-facing snapper, particularly to support the video calling system FaceTime in high definition.
FaceTime will soon be allowed over cellular in the iOS 6 mobile operating system upgrade (more on that below), meaning Apple might see it as a good time to boost the quality, particularly if the phone is offered in 4G (see more below also).
Another area of expected improvement is the battery life. Widespread criticism of rapid battery drain in the iPhone 4S led the firm to release a number of software updates, but many users still reported problems, and complained about always needing to be close to a charger.
It is therefore likely that Apple will use the new space freed up in the redesigned iPhone body to boost the battery, ensuring the smartphone can cope with the faster processor, high-quality screen and demands of daily usage.
Apple beat rival firms including RIM and Nokia earlier in the year to get its proposed new SIM card design adopted by the European Telecommunications Standards Institute (ETSI), which sets technology standards across Europe.
The firm had already gained support from various major mobile carriers for its super-slim technology, known as the "fourth form factor (4FF) card", which is 40% smaller than the current smallest SIM card design.
Larger SIM designs take up valuable space inside mobile devices, but Apple's technology is just 12.3mm wide by 8.8mm high and 0.67mm thick, whilst still offering all the same functionality as current SIM cards.
After the Apple nano-SIMs were spotted at a German retailer this week, it is now widely expected that the iPhone 5 will launch the technology.
After launching a 4G iPad in the US and Canada earlier in the year, Apple is widely expected to do the same with the iPhone 5, enabling users to access superfast mobile broadband speeds of up 100Mbps on their handsets, compared to just 5Mbps on 3G.
It is almost certain that an iPhone 5 4G LTE will be announced for the US, along with certain other markets, such as Canada, Japan and possibly Australia. But its arrival in the UK is far from certain.
Yesterday, Everything Everywhere launched the UK's first 4G network in test phase in four UK cities, with plans to expand that to 16 urban areas by the end of the year, reaching 20 million people.
Everything Everywhere also unveiled its new EE brand, which will market the 4G LTE service to customers and sell 4G handsets in Britain, such as the Samsung Galaxy S3 and Nokia's Lumia 920.
Apple is expected to announce a 'pentaband' iPhone 5 later today, meaning it can accept up to five radio frequencies. If EE was able to get its adapted 1800Mhz frequency for 4G accepted by Apple, then it would get the major boost of being first in the UK market with the iPhone 4G.
However, Apple was hit by criticism and even fines after it marketed the new iPad as 4G LTE in the UK this year, as the tablet could not actually connect with 4G networks.
As EE's 4G network does not have majority UK coverage and its overall 4G plans could still be hit by a legal challenge from rival O2, Apple may wish to err on the side of caution and hold off a 4G iPhone launch with EE.
However, with an expected network reach of 20m by the end of the year, bringing the iPhone 4G to Britain could still prove attractive, particularly as key rival Samsung is already there with its Galaxy S3 LTE. But Apple will certainly have to be more careful with its marketing...
In June, Apple announced the iOS 6 mobile operating system and it seems pretty clear that this will run on the iPhone 5.
There are many new features in the mobile OS, but the headline grabbers were improvements to voice assistant Siri to offer more detailed information and recommendations, along with deep integration of social network Facebook in apps and other iOS services, similarly to the way Twitter is already integrated.
Apple also intends to launch its own proprietary Maps system as a replacement for Google Maps in all newer iOS devices. The Maps app features turn-by-turn navigation with Siri support and dazzling 3D flyovers of many major cities.
Alongside Google Maps, Apple intends to give the cold shoulder to Google's YouTube by not pre-loading it as an app on iPhone and iPad, prompting the video sharing site to launch a revamped iPhone app.
Various leaks have suggested that the iPhone 5 front-facing camera has been moved to the centre-top of the handset, fitting with fit with speculation that the phone will come with an NFC chip.
NFC enables someone to transfer data between a smartphone and a contact point with just a 'tap', and is often used for mobile payments in shops, cafes or train stations.
Despite NFC being embraced on handsets running Google Android, including 106m NFC-enabled Android cellphones being sold in 2011 alone, there is a feeling that the potential of NFC has so far remained largely untapped. It is thought that Apple now wants to really drive the market forward.
As it already has a vast database of users' credit card details via iTunes, Apple could quite easily set up a system involving users making wireless payments, and then partner with the major retailers. This could be the moment NFC goes truly global.
A possible hint to the firm's plans comes with the new Passbook app, which allows users to use their iOS device to redeem coupons, movie tickets, boarding passes and loyalty cards, as well as conduct other financial transactions.
Jack Kent, senior analyst for mobile at IHS, noted: "With its capability to tie purchases together, Passbook will be an effective tool for managing mobile transactions, mobile money services and mobile commerce.
"If Apple combines Passbook with its new location platform, the company will open both a new revenue stream and a new competitive front with Google."
Kent said that Apple may choose to partner Passbook with new hardware support in the iPhone 5, such as NFC.
Documents recently revealed in financial disclosures revealed that Apple was in a hell of hurry to complete its $356 million (£232.7m) acquisition of AuthenTec, the maker of finger-print recognition technology for mobile devices.
This has led to speculation that Apple's new iPhone could feature the technology as both a security feature and to unlock additional functionality. Finger-print recognition has been seen before in electronic devices, but it is understood that AuthenTec's technologies enable users to set different tasks for different digits.
In theory, this would allow the user to unlock their phone with their thumb, but then access their email with an index finger.
Of course, AuthenTec makes other security and network technologies aimed at business, and so Apple could instead have wanted the firm for its growing enterprise arm. But its a pretty darn good rumour...
Apple rather underwhelmed with its annual iPod line revamp last year, but that is all expected to change in 2012. Headlining the rumours is a potential new premium iPod Touch model that would feature the same rumoured 4-inch display as in the new iPhone.
It is thought that this premium model would come with a Retina screen and faster A5 processor, although it may be that Apple will not want to give it exactly the same core specs as its more valuable iPhone.
Also in the rumour mill, the iPod Nano is expected to no longer come in its small-square form and instead be slightly taller and come fitted with a home button as featured on larger iOS devices.
According to 9to5Mac, the budget iPod Shuffle will get a slight refresh with expanded colour options.
It has also been speculated whether 2012 will be the year that Apple finally drops the iPod Classic, after more than a decade of sales for the MP3 player that started it all for the firm.
There have been rumours that Apple would announce a new smaller iPad on the same day as the iPhone 5. Often called the "iPad Mini", the new tablet is expected to have a 7.85-inch screen and slimmer side bezels, making it appear similar to a large iPod Touch.
It is thought that the iPad Mini would compete with Google's Nexus 7 and Amazon's Kindle Fire, both of which have taken market share from the 9.7-inch iPad due to their cheap price and big content libraries.
However, as the iPhone is such an important product to Apple, it now seems unlikely that the firm would want to steal the spotlight with a brand new product. Instead, it is expected that Apple will hold a separate iPad Mini launch event in October.
So, when can I get my mitts on the iPhone 5?
It is widely expected that Apple will announce the start of pre-orders immediately after completing its launch event in San Francisco later today. If the firm follows previous patters, this would mean an initial launch in key markets, including the US, UK, Japan and Australia, followed by a further roll out in other nations towards Christmas.
Apple tends to prefer to launch new products on a Friday to give a full weekend of sales. As US communications giant Verizon has cancelled all holiday between September 21 and September 30, it is thought likely that sales will begin on Friday, September 21.
In terms of price, if Apple follows the iPhone 4S model, the phone will come in either black or white and cost $199 for the 16GB model SIM-free and 32GB $299, while the 64GB version will be priced at $399. It is unclear whether the LTE model will cost more.
Of course, though, this all speculation and we will only know for sure later today. Apple's press conference starts at 10am local time (6pm UK time) and we will be live blogging at the London companion event, so stay tuned.
Photo gallery - the history of the iPhone in pictures:
Copyright: PA Images Paul Sakuma/AP