[tacticalogic]

I assume that since there is a VOIP PBX for Linux (http://www.asterisk.org/) that integration would not be too hard.

Integrating with that one might not be too hard. Integrating with existing proprietary systems like Mitel or Cisco is likely to be a much tougher nut to crack.

[taxcontrol]

Agreed, though in the worst case, dropping to a PSTN interface and transferring the call to another system’s PSTN interface might work. Cumbersome though.