I have a VG224 registered via SCCP to CCM6.1. From FXS to FXS on the VG224 the calls are fine, but from FXS to IP phone I only get one way audio even though DTMF tones pass through in both directions. The VG224 and the IP phones are on the same vlan and so I don't see this being a routing issue. Any idea on what to troubleshoot?