Some good suggestions. Thanks.
BladePilot- I'll try getting the phone unlocked and see if that helps. I'll try the o2 sim card in an old unlocked phone first to check that the SIM is happy to work with any phone. This should detect whether I'm risking souring my (frankly already thoroughly curdled) relationship with o2.
sooty- Thanks for the suggestion but I think I've tried that. It's what I was trying to explain in para 4 of my original post (21 May)
JofM5/GreenGranite- That's a cool way of getting to the internet, but is it really any different from the "geographic number solution" as suggested by sooty and already tried by me? I'm not convinced that the phone would still let data go out over the bluetooth. Might be worth the investment if all else fails. (Though if it gets that bad I'll ring the office and get them to read out the NOTAMs and Wx!)
Sh3113y- Changed it to "GSM". Still no joy.
I'll let you all know how the unlocking thing goes. Thanks again
Phil