Oh yes your right, for some reason it set back to 5060. I've now changed it to 5061 and it all working!
Typical I looked at the log, and I overlooked the simplest factor!
One little factor outstanding, which im not sure if you've got but the phone's call time counter starts ticking over soon as the number is dialled, rather than when the receiver picks the phone up.
Thanks so much for your help.
Have you found that the unit is reliable for every usage?