[OpenSER-Users] Media control with openser

Hello all, Actually i have openser box which i used to make calls among my offices which spread different geographical places. i am using in the configuration file just to make changes to my rtp packets so without RTPPROXY and MEDIAPROXY modules i was able to make calls even my end UAC are behind NAT. but if i want to control my media between different UAs like a prepaid system as we used to see in case of mobile prepaid system which stops you from continuing your call when there was no balance left on ur mobile . can anybody give me a hint how can i do that ? if so what architecture it needs like any mediaproxy? will session border controller help me out? just give me a hint so that i can go ahead thanks once again -- Srinivas Antarvedi