External calls with Call Manager from VPN connections

We recently installed Cisco Callmanager for VOIP in our main office.  Our VPN employees can call into office and it works fine. But when VPN employees can make connections to other VPN employees or POTS, their is no voice connection on either end.   VPNs are routed through a PIX Firewall and all three VPN employees can see the call manager server.   Installation company thinks it is something in our firewall.  Any ideas?  
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Let's clarify.
Suppose you have an Office user and Remote user.

1) connection from Office to Remote is OK from voip to voip terminal
2) connection from Remote to Office is OK from voip to voip terminal
3) connection from Remote1 to Remote2 is broken
4) connection from Remote to office is brotek from voip to pots termilal

is it?

If it's correct, problem 4) is in Cisco CallManager or voip gateway configuration
problem 3) may be in Cisco or may be in firewall. For shure try the following:
Remote1 has IP1
Remote2 has IP2
Try to connect directly from Remote1 to Remote2 via netmeeting application using IP addresses for destination if this works, the problem in Cisco, else in firewall. Netmeeting is standard for all Windows and resides in Program Files/NetMeeting/conf.exe


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