For its National Mobile Report 2012, Ofcom-accredited Billmonitor.com analysed more than 69,000 real mobile phone bills and found that 26 million mobile subscribers in the UK are on "excessive tariffs".
The website said that these people - representing 74% of UK mobile users - are wasting on average £164 a year on allowances "three times too large for them".
Billmonitor.com said that if mobile users adopted a "tariff diet" approach, they could collectively save £4.32 billion.
Of those on "excessive tariffs", two specific groups were identified, each with their own area of key wastage.
Big Surfers, for example, use lots of mobile data while accessing the internet, but make few calls, while Big Talkers do the opposite.
The report identified that 12m people could save £2.09bn by slimming down their oversized calls & data allowances.
Some 8m people could save £1.14bn by slimming down oversized data allowance, and 6m people could save £1.09bn by slimming down oversized calls allowance.
However, around 8m subscribers actually need the opposite, as their chosen tariffs are too small for their needs, costing them £1.66bn in extra fees.
Dr Stelios Koundouros, the founder of billmonitor.com, said that millions of mobile users could benefit from going on a tariff diet.
"At a personal level, the right solution for you depends on the precise mismatch between your usage and your tariff," he said.
"billmonitor's new free-to-use Bill Check-up service helps you find out exactly where the 'waste' in your contract is occurring and remedy that with a match to the right contract - whether you're locked into a long-term contract or you're free to switch to a new contract.
"By offering personalised, accurate insights into usage habits, billmonitor can help guide people towards much-needed savings on their mobile bills."
The report also indicated that one in five consumers are 'mobile addicts', who can't live without their device and tend to be the highest individual wasters.
> UK consumers wasting mobile data allowances
> Mobile users wasting £4.9bn on contracts