Let me offer wide range of different voip software for you. You can buy or rent:

PortaOne Bill, SIP and UM MR15
MVTS/SIP-HIT 3.1.3
MVTS II
Nextone 4.1
Sysmaster VM2000 5.06
Sysmaster SM7000 2.0.58
Unibox (VM and SM at one server)
VoipSwitch 2.0.943
RBS VoIP from Alepo 6.1
SIP and H323 softphones
and other

I will help you to make the best choice exactly for your needs. Let me know your requirements and you will get the solution that overcomes your expectations.

All your inquiries are welcome at ipmiracle@gmail.com (MSN, e-mail, googletalk).

Best wishes,
Roby.