New facility - new phone system

I am more than willing to figure out how Asterisk works and set up a system for us, but I need to know if some of my equipment would work with it first.

Quick backstory 1: We just purchased an ATT SYN 248 phone system a couple of years ago. The phones are ATT-SB35031 and the box is the syn 248.

Quick backstory 2: We are opening up another building down the road that we want to have integrated to our phone system for calls and overhead paging.

Quick backstory 3: Someone I know online was telling me that Asterisk is a good solution for this.

I am knee deep in figuring out a bunch of other things and I am getting it just fine but I cannot seem to confirm whether or not I would be able to use our existing and basically brand new SB35031 phones if I have a VOIP gateway for the phone lines instead of the SYN248 box using Asterisk on a server.

I would set up a VPN gateway between the two sites etc to accomplish the networking part, I just don’t know for sure if the phone itself would be usable…

Any thoughts?

I can’t find any information that suggests those AT&T phones may be used generically, with Asterisk, rather than with the AT&T gateway device.