FlyNumber provides virtual numbers all over the world and can work with ANY VoIP provider.

If the Provider has a SIP uri ( that isn't firewalled or limited) we can send the calls there at no additional charge

You can easily set up our service with Callserve. They've provided us their SIP URI to make things easier for you. You enter the username with Callserve at the signup form and that's it. 

Callserve
Callserve
http://www.callserve.com/

Call forwarding prices:

Monthly price: 0.00 USD
Setup price: 0.00 USD

FlyNumber offers an extensive selection of international DID numbers. In addition, we are constantly expanding our services so as to increase the number of regions supported, as well as to increase our coverage in each region.
With an advanced network structure and innovative products, we are ready to bring high-quality, cost-effective and reliable service to our customers all over the world.