Can I use a Cingular Sim Card in a T-Mobile Phone? (More in Details)?

No. SIM cards are carrier-specific. Not going to work.

Yes it says because it locked to network...T-Mobile....You have to unlock it from network lock to use Cingular sim card in the phone.You can Unlock it using the free unlock code.Get the free unlock code for DCT phones at here Unlock-free.com and unlock it from network lock ....