One of the coolest features of the new iPhone 4S is Siri. The virtual assistant will let the user do all sorts of things using their voice alone. Siri will text for you, find the local weather and lots more. Siri does use the data connection on the iPhone 4S to reach its servers back at Apple though. The heavy use of Siri has reportedly put a big strain on some mobile networks.
Bloomberg reports that data use for iPhones has doubled with Siri. Take the doubling of data with all the new users that the iPhone 4S is attracting, and you get a lot of new data use on mobile networks.