Ip phones dont hear the beep when leaving a message

[beth08]

Hi,
Strange query but we have an issue that when a user calls from their ip phone to a mobile and gets the voicemail saying pls leave a message after the beep, they dont hear the beep, so dont know when to leave their message.

This works however from other non-ip phones in the same building, in that the caller will hear the beep for teh same voicemail previously tried.

Anyone any ideas - very weird!

thanks!

 

[MagnaRGP]

What codec is being used? If G.729, try turning of the VAD.