Tks for the feedback Zing. We have just been to the shop and they had the same problem with this card on our phone and another of the same type straight out of the box. They then tried an 02 SIM which they had behind the counter and the relevant message centre no. appeared in the phone automatically. This seems to be the root of the problem - for some reason it seems the phone isn't reading the SMS MC number from our SIM and won't let us enter it manually. Does that make sense?? We've just tried calling VM customer services but, having explained it all to her in some detail, all the operator could do was recite the same CN that we've been trying to use. Anyway, she's kindly arranged for the technical team to call us to try to sort it out so we'll see what happens in due course.
While we wait up to 72 hours (hope that's not WORKING hours!!!) for the call, any more advice or suggestions on this would be very welcome.