I had the $30 one too (Android was already added) when I had this issue - that is what is so frustrating. After I made sure that my account showed the S2 as my phone, I went to the "change services" chose the $20 data plan (even though I already had the $30), then confirmed the switch. I then went back into the change services and switched back to the original I had previously. It took 2 minutes and started working again. It acted as a "reset" i guess.
Calling Tmobile was just a pain in the but for me and the wait was way too long so I tried my own options and this worked just fine. Was a lot quicker than waiting for them too. Plus, the Tmobile rep in the store already said I was good to go when she switched my sim card to the new phone and checked to make sure everything was good. I knew I would still have the same services previously, but I asked anyway if I would still have unlimited texts, unlimited data plan, etc. and she said yes, "you do not have to do anything." My previous phone was the G2.
I am sure calling will obviously work too, but this proccess took a couple minutes and didnt cost anything - no money or wasiting time on the phone.
Calling Tmobile was just a pain in the but for me and the wait was way too long so I tried my own options and this worked just fine. Was a lot quicker than waiting for them too.
You can get the same effect by using the online chat.
I guess what people aren't realizing -- if you change your data plan from A to B, you have the potential of losing your grandfathered unlimited data. The grandfathered plan (before they listed pre-throttle limits) are 5GB pre-throttle for the same price as the current 2GB pre-throttle.
omg, i just realized this at the bottom of the confirmation page when i changed the data plan...
We’re sorry, but we're not currently able to complete your request online. If you have questions, or if you’d like to change your plan or services, please call Customer Care at 1-877-453-1304 or dial 611 on your T-Mobile phone.
I have the same issue with my Galaxy S2 after using a Samsung Dart for a week. Have tried chatting with support and no one can help. I have tried most of the suggestions above but there is no change. I did try to change my plan online and it is pending. I have since tried to cancel but can't. I do not have the option to change my data plan else I would try that as well. Not sure where to go from here. When I search for available networks only AT&T shows up. I have the correct sim card according to support.
I have selected under Mobile settings:
Use Packet Data - checked
Data Roaming - checked
Access Point - epc.tmobile.com
Network mode - GSM/WCDMA - Auto - checked