VoIP - calls get through but no voice

[telesonic]

We have two 403's with VCM5's linked via VPN's, with remote workers on two hardphone extensions from site A. Callers between the two sites can call and talk ok. The home users can call in to people at site A ok.
However when the home workers try to call an extension at Site B the 2050 rings but no voice is coming through.
What differences are there in this type of call? What can I try to see on a monitor trace that may enlighten me??

 

[Morrack]

Review your IP Routes on both systems. Ensure you can ping endpoint to endpoint - from a PC at a remote workers house to a PC at Site B's LAN.

Failing that, suspect a firewall problem, probably at Site A.