I would totally consider the Fonality trixbox Appliance.
I know we have some hardcore IT people in our audience, so check out this hot box of Asterisk-based IP-PBX open-source telephony action. The appliance comes loaded with Fonality’s trixbox software platform and is wrapped in an industrial-grade, rack-mountable server with dual hard drives and dual power supply redundancy options. Use it with VoIP, E1/T1 or up to 48 analog lines. And it’ll only set you back $999.