Missing audio stream from IP phone over IPSec tunnel

I am currently using a Vonexus VoIP server connected to a Cisco 2811
router. The router has an ISDN PRI for voice calls and a 4Mbps
ethernet connection for data. I have set up an IPSec VPN tunnel to a
remote site connected with a Cisco 1721 router with a standard T1. I
have installed a VoIP phone at the remote site. The phone registers
with the Vonexus server fine, and calls can be made to and from the
main site as well as from external phones i.e. my cell perfectly fine.
However if a call is made from the phone at the remote site to an
external number the audio from the VoIP phone cannot be heard. Has
anyone seen this before or have any tips? More detail can be provided
if needed.

Thank you

Todd

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