there are few ways to record VoIP:
1)passive, by configuring the network with spann / mirroring session, transfering the phones or Media gateway to the recording NIC within the VoIP Logger, (IP packets)
2)active, such as Avaya DMCC / CMAPI, Cisco Active, Nortel DMSIP - the packets will send to the recording NIC from the PBX / phone side, requires license and cost more, but can ovr come issues with passive recording
hope its helping you