Voice Data Interception in OpenBSC

Hello, We are trying to use OpenBSC to build a few prototype services for a GSM network. As such, I need to know where in the code I can intercept the voice data that is received from an MS in the BTS. Ideally, I would like to have intercept points in the outgoing (to MS) and incoming (from MS) at the BTS in software. Note: I have just started to read the source code of OpenBSC, and as it is quite extensive, a few pointers will be useful. Feel free to correct me if I'm way off base here. -Earlence