If one of my clients dial their other office, & a mobile for conferencing the internal call gets cut off.
If they are dialling within the same office & a mobile then the call is successful.
So it appears just dialling to external causes the issue!! Any ideas as to what to check? It is call manager 4.2
This really sounds like a codec issue. Could you please elaborate on your topology? Are you using G.711 within your office and G.729 with the remote/PSTN sites? Are you using Hardware Conferece Bridge or Software Conference Bridge?
Are you using CCM or CME? What version?
You need to include as much details as possible, perhaps some configs.