Would features on smart phones be limited? I'm looking at getting a MyTouch Slide or a HTC HD2. It seems like if I just had an active SIM card I could stick it in any phone and it would work no problem right?
If the phone which you are getting is free from network restriction or if it has been locked to T-mobile network, then you can use your T-mobile SIM card with it. You won't be having any limited features in accessing it. If your phone is locked to some other network, you need to unlock it in prior. Only then you can use your Tmobile SIM card with it. You can get the unique unlock code for any mobile phone model from Mobile-Unlocker.com at affordable cost with an easy unlocking guide. Good luck.