All voip solutions

if I am right, with openser+sippy ,it can support prepaid billing .sippy can make sure all sip messages(invite,bye) going through sippy,so sippy can know all call status ,he can send authentication,authorize,accouting when call invite,bye received,and interworking with external radius .
I saw openser has ability to send bye to one call when max call time is exceed.

problem is how to play balance or ivr ,etc when in callingcard solution.I think we still need asterisk or freeswitch or SEMS . below is sippy b2bua features :
* 5,000-10,000 simultaneous sessions per server;
* 150-200 call setups/tear-downs per second;
* Realtime calls control and call data records (CDRs) generation;
* Optional ability to use Sippy RTPproxy for media relaying;
* Optional ability to perform Cisco-compatible RADIUS AAA (Authentication, Authorization and Accounting);
* RFC3261 compliance;
* Seamless compatibility with majority of popular SIP software and hardware on the market today;
* Robustness and Resilience;
* Simple and clean, yet flexible, internal design making implementing new features and services easy;
* B2BUA could be easily combined with other Open Source software, such as SIP Express Router to build complete softswitch solution.