Our setup is like this. IPC PBX has a Qsig E1 on VG which is connected to PSTN and CUCM. Unity 5.1 has SCCP integration with CUCM for ip phones and SIP integration for IPC phones VM. Incoming calls from PSTN easily transfers the call to VM for IPC phones on either busy or no answer. However, if a call is placed to the IPC phones from Cisco phones, it continues ringing the IPC phone without transfering to VM. Is it something wrong with the IPC PBX ? how it works for PSTN but does not work for Cisco phones ?