Hardware Recommendation?

I was wondering if you could help me out with a hardware question. We are running Asterisk 1.4, Free PBX 2.8, PBX in a Flash and iSymphony.

In addition, we have a dual-span T1 card with a T1 and a PRI connected to it, all supporting a 30 concurrent user call center. Bria softphones are on the desktop.

What hardware specifications would you recommend for a server running this combination of software and hardware, supporting this many users?