Can anyone help with my 8525?

Here's my problem:
Cingular was good enough to provide me with the subsidy unlock code for my
8525. The instructions said to put in a non-Cingular SIM, boot up the phone
and wait for a prompt to enter the code. So I put in a T-Mo prepaid SIM
(which is the only non-Cingular SIM I could readily get my hands on). When
I turned the phone back on it booted normally and proceed all the way to
opening my Today app't screen. It did NOT give me prompt for unlock code.
However, the phone cannot make or receive calls with the T-Mo SIM and my
attempts to open the Phone icon to get to the phone settings yield this
error message: "Phone is not ready. Wait 15 secs and try again". But
waiting does not make things better. The T-Mo signal in the area is strong
so that's not the problem.
So anybody know what's up with my phone? Why is there no prompt for the
code? Is the phone already unlocked and Cingular is have a joke at my
expense? If so, why won't the T-Mo SIM work? I was hoping to use the phone
in Europe using local SIMs. But now I don't know what I've got here. Any
advice or observations are much appreciated.
--Iopsy