[OpenSER-Users] OpenSER Question

Hello, I wanted someones honest opinion. I have ran across and read a little on SER and OpenSER have not yet had much time. But would you recommend OpenSER for a service provider who is wanting or thinking about deploying VoIP service for its customers? What other products would you recommend to work along with OpenSER such as billing and accounting interfacing. We have used Asterisk for our internal PBX for about two years and love it. Or would you recommend staying with a commercial product like Cisco or Sonus? We prefer open source since our base will be small to start and not large enough to justify a Sonus which is the preferred commercial product. Any advice is definitely appreciated. Otis.