[Thanks to everyone who sent this in]
Update: T-Mobile has responded with a clarifying statement we've added after the break. There will be no surcharges for use over 500MB per month, but once you cross that line, any downloading activity will be "restricted." By which the company seems to mean "restricted to whatever WiFi connection you can scrounge up," because its 3G airwaves will be off-limits.
Changes to Mobile Internet fair use policies
T-Mobile is the only operator to give customers the Mobile Internet for a fixed-price. We never charge our customer's more than they expect for their Mobile Internet in the UK.
Therefore you'll never need to worry about how many emails you've sent, how long you've been on-line or the 'data / GB's'
Browsing means looking at websites and checking email, but not watching videos, downloading files or playing games. We've got a fair use policy but ours means that you'll always be able to browse the internet, it's only when you go over the fair use amount that you won't be able to download, stream and watch video clips.
So Whats Changing? - From 1st February 2011 we will be aligning our fair use policies so our mobile internet service will have fair use of 500MB.
What Does This Mean? - We'll always let you email and browse the internet and you'll never pay more than you agree to. We do have a fair use policy but ours is there to make sure we deliver the best service possible to all our customers. This means that you'll always be able to browse the internet.
So remember our Mobile Broadband and internet on your phone service is best used for browsing which means looking at your favorite websites like Facebook, Twitter, Gmail, BBC News and more, checking your email and looking for information, but not watching videos or downloading files.
If you want to download, stream and watch video clips, save that stuff for your home broadband.
"Yesterday we began notifying our contract customers of changes to their Fair Usage Policies (FUPs) relating to data usage on mobile phones. In line with the industry, T-Mobile will be reducing its FUP for data downloading to 500MB/month from 1st February 2011.
"These restrictions will affect both new and existing customers, and will ensure an improved quality of service for all of our mobile internet users. As the average mobile internet customer uses only 200MB of data each month, this will only affect a small minority of users, whom we have begun notifying.
"T-Mobile will not charge its customers additional rates for exceeding these data limits, and those who do will still be able to access important services such as email and website browsing, but will have file downloading restricted. Customers who have a need for higher volumes of data will be encouraged to take up a separate mobile broadband plan. We are confident that these changes will result in a better experience for all of our customers who use internet on their phone."