Well from what I know with Verizon, the blackberries dont run off the sim cards. The sim cards are basically to make your phone compatible for internation traveling and to store contacts. You need to call T-Mobile and have them activate the phone if they can. When I bought a Tour on eBay I kept my old sim card, but they just needed the information on my blackberry to activate the phone with my number. So basically you cant just stick a sim card into your phone and expect it to work. I hope that helps! Good luck!
Usually you can just stick your SIM card and it works. Occasionally you'll have to maybe put your carriers service books on it, but other than that it's pretty simple.
It should be very easy to do. I have a tour running on T-mobile and verizon at the same time. What I did is call Verizon and unlock the tour. I told them I was traveling to Europe and then they unlocked it for free. Next I bought a prepaid SIM card from T-mobile.com. Stuck the card in and changed the mobile network under options to GSM. That's it. Switch back and forth as much as I need. Now getting the internet is a much more complex job, but can be done also. If you need that search these forums.
Posted from my CrackBerry at wapforums.crackberry.com
This is a know issue with the storms and i assume will carry over with the tour when using tmobile sim cards. The official word from RIM is that because tmobile does not service books designed to work with specific operating system versions, you may occasionally experience the circuit/channel issue. I myself had a storm and used my tmobile sim card in it and had no problems. The problem seems to be related to geographic location, we would have frequent complaints of I am traveling and am now having this problem. Those who actually have a Blackberry data service plan seem to have less problems, but it is indeed a known issue that tmobile is aware of, as of yet tmobile's solution is to use a tmobile approved phone, which is a cop out because i make iphones work perfectly, mms and internet for tmobile but they dont want to touch the bb's.