I just read a sad piece of technical journalism from Charles Arthur for the Guardian. I'll resume his rant; he blames p2p (file-sharing) usage for the new "no more unlimited mobile networking" policy that apparently O2 is moving into. He cites an O2 blog post which actually makes no mention of this.
According to the very imprecise graphic 97% of the users consume less than 500MB a month, the average would be 200 and 0.1% use more than 690MB. In short, very very few people tend to exaggerate IP (data) usage. If that caused any real nuisance to the network that would mean that either the operator's network is insufficient and/or they do not have the knowledge to implement simple QoS regulations (example: slow down the speed when network usage goes up so that all traffic can be on the move). So what is the real deal here ? Why are operators no longer happy to offer unlimited data for a fixed price ?
My conspiration theory is as follows: Now that you can access the Internet via your mobile device you can trade limited "text messages" (SMS) for unlimited text via realtime chat (irc/msn/aim/icq/etc) or email, you can trade phone calls for VOIP (skype, etc). And all this being on The Network (Internet) means that there is no difference between local and long distance communications. This is precisely, in my opinion, the real part where the operators may feel cheated. Users can escape the overcharges of calls and text messages not included in their plans, and why not even get a minimal call/text deal and just go for the unlimited mobile internet.
In reality the very few who actually do use p2p networks (illegal or legal btw) are not a real nuisance for the network, they are instead, AS USUAL, an excuse to change policies, pricing and laws. In this case, it's actually a "technology journalist" ranting about this, as if 0.1% of the data/phone users stole directly from his pocket.
Oh, and one more thing, I'm pretty sure those statistics include users who bought the mobile Internet dongle thing, you know the 3G usb device intended to connect computers to the Internet, in that case it's more than normal to go over 690MB in one month..