I"ve set up SIP trunks with various carriers in the US: AT&T IPFlex, Verizon Business, Callcentric, etc. for multiple customers, including US Federal Courts, a Georgia State Agency, Intercontinental Hotels Group (IHG), Genuine Parts, etc. My specialization is Cisco VoIP, and I'm very well versed in Cisco CUCM and CME solutions as well as Cisco CUBE (Cisco Unified Border Element). From the skill requirements for this project, it appears that you are running an Asterisk PBX. If you can provide a person knowledgable in Asterisk, we can make this work.
One of the projects that I completed in the past was a Proof of Concept design for Ulta Salons to integrate a centrally deployed Cisco Unified Communications Manger (CUCM) with Vertical PBX deployed in each of their stores. I worked side-by-side with a Vertical PBX engineer, so I was configuring the Cisco side and he was configuring the Vertical PBX side. I have done similar work integrating a Cisco Unified Communications Manager system with a Mytel system at a Georgia State agency, where the Mytel side was handled by a Mytel engineer. I've also integrated CUCM with an Avaya IP PBX at a Fortune 500 company, working side-by-side with an Avaya engineer.
If you have a knowledgable Asterisk person to work with me, we can successfully complete this project. If we don't make this work, you don't pay anything.