Network analyst Arieso claims that the voice navigation software could see users incur significantly higher bills, and mobile networks struggle with the volume of data being transmitted.
Arieso reached the conclusion after analysing the data usage of one million smartphone owners on an unnamed European network.
As well as finding that the iPhone 4S uses twice as much data as the iPhone 4, the study suggested that BlackBerry users consume 20% less than owners of Apple's latest handset.
Apple released the iPhone 4S with Siri on board in October. Similar voice navigation software has since appeared on the Android Market and other mobile storefronts. Earlier this week, the Ask Ziggy app brought such functionality to the Windows 7 Phone.
"What makes Apple unique is that they have done it first successfully," Arieso's chief technology officer Michael Flanagan told Bloomberg.
Apple is yet to comment on Arieso's findings.