I had an issue with cyberoam where calls in had voice both ways, but calling out they could hear me, but I could not hear them, i.e. inbound RTP voice traffic was not being forwarded.
Virtual server was setup with port range to forward 10000:20000, firewall rule was configured with WAN to LAN rule to allow from any source port to the destination.
This was confirmed by checking diagnostics were showing incoming packets were being received but rule 0 was applying so packets were not forwarding. Contacting
cyberoam support they ran this command from the console
cyberoam system_modules sip unload
and then voice worked!