Custom OpenSIPS Application

We provide SIP trunking and Hosted PBX services to small business. Currently our "edge" server is based on Asterisk/A2Billing. We are considering migrating to an OpenSIPs/FreeSwitch based solution if it will offer greater scalability, and reliability. A2Billing is currently working very well for us, and we like the fact that it is a "system" that has a good feature set and cohesive interface. We are bringing a second location online for physical redundancy and we'd be interested in moving to an OpenSIPs/FreeSwitch based platform. The system must support seamless failover between locations in the event of an outage. We already have an existing customer base, so we're not open to unproven systems. We are only interested in developers that can demonstrate that they've deployed similar systems. As defined in the attached document, the system must have all of the basic features to provide SIP trunking service (DID routing, authentication, reporting, LCR, etc). An integrated billing system or customer portal is a plus, but not a requirement day 1. The budget for this project is relatively low for two reasons: 1 we are only considering proven solutions. Development should be minimal because the successful developer will already be able to utilize his or her previous work. 2 we already have a perfectly functioning system, so the new system must be inexpensive to justify the change. While this project's budget is relatively low, the potential for additional work is extremely high. The last two developers we worked with on similar projects were awarded several thousands of dollars in additional projects