Default Can my unlocked Wallaby work with the Cingular GSM network?

Hi, I have a Siemens SX56, unlocked with the tools I found here. However, I can not use my Cingular SIM chip, only a T-Mobile (or ATT) one.

Is there any way that I can do something to get my device to work on the Cingular GSM network?

Your help is greatly appreciated.

Thanks
Cen