Thanks for the advice on non-Nokia phones, but that's not really the question. I've had Nokia phones for 10 years - 6110, 62210, 6310i - they were given me by my employer. They all still work, despite being physically abused. The user interfaces are essentially the same and all the batteries are interchangeable. And as Andy says, I can easily unlock them myself.
Does anyone know if GeoSIM use some bona-fide STK API to initiate callback when you press 'call' (I assume that's what it should do - i.e. prefix the *125*1 etc and genererate the USSD message) or is it some sort of hack - which might work or might not? I have rarely seen a spec for a Nokia phone that says it 'supports STK' - though some obviously do - or what level of STK support it offers. Reviews don't usually mention STK. Perhaps STK is actually more likely in a low-end phone where its use is pre-programmed.
This list
http://www.qred.co.uk/phone_compatability.htm suggests a 6230 will work but a 6230i won't. Why on earth might that be? Did Nokia deliberately remove the facility, or did they break it? Maybe they include STK if there's space in memory and take it out if something sexier - like a camera - is added.
Dave