You didn’t give much info.
The 912 is a multiservice gateway, has a ton of functionality.
You say it’s a T1, do I assume it’s a data T1 and the current carrier uses the 912 as a gateway for the voice (either PRI or analog)? Or is it an IP gateway and they connect SIP to their network?
If it’s converting to analog or PRI you might want to see if their current carrier supports SIP trunks so you don’t need any hardware.