Our Voice network and Data network are on separate switches. Not converged. Voice network has a Cisco Catalyst 3560 POE switch, Cisco ISR 2821, Cisco UCM6.1 BE, Cisco IP Phones. The Data network has Linksys switches, Desktop, Servers, Exchange 2007 Server with UM. And networks are connected together via a Gig connection.

The issue is while listening to voicemail messages from the IP phone or Outlook they are most often garbled or disjointed or dropped sections; therefore we don't get the complete message and find that we miss the persons name or contact info for example.

We have QoS implemented on the voice network and no QoS is enabled on the data network (Linksys switchs) where the voicemail message call flow is going through.

Any ideas and suggestions for what could be going on here including any specific troubleshooting?

Thank you!