OP - you should clarify which upgrade program you're speaking of. The
Apple iPhone Upgrade Program can only be done directly through Apple online or in one of their Apple stores. You would not be charged an upgrade fee by T-Mobile if you did this as the device purchase is outside of TMO. I have swapped SIMs as well as activated the SIM that came w/ the upgraded phone and I have never ever been charged an upgrade fee.
I assume
@dooku77 upgraded through T-Mobile's program and was charged.