Guys, I think this trumps everything. You may have to call the 800 number, but T-Mobile is making this right with those who purchased with the $10 plan:
http://newsroom.t-mobile.com/phoenix.zhtml?c=251624&p=irol-newsArticle&ID=1872166&highlight
Q. What was the $10.00 per month fee we heard about on launch day?
A. We had an executional error in our system at launch that created an erroneous $10.00 charge for network access. We have worked in the days since launch to correct this issue in the system and through employee training. There is no $10.00 per month fee for the 200MB of free data. We are crediting any customer that was erroneously charged this fee.
I am pleased. This is in writing, and it's also in most of our accounts - at least those who have already called.
Yay finally some kind of confirmation that isn't over the phone.