I was finally able to get T-Mobile to e-mail instructions for unlocking
my cell phone.  The instructions read as follows:

1.  Place a non T-Mobile SIM card into the handset
    and turn the handset on.
2.  The handset display should read "Enter Special Code".
3.  Enter the unlock code and press "OK".

Question:  Could something bad happen if I do steps 2 and 3 while my
current T-Mobile SIM card is still in the cell phone?

Thanks.