Hey, that is really helpful slyfox - many thanks
Not knowing a great deal about cell phone models, I did a quick Internet search. The Nokia 6310i was clearly a well respected phone in its time and there are plenty around on eBay for very modest prices... so I reckon that is probably the route for me.
I'll confirm the adaptor compatibility and post back on this forum. I guess there will be at least some other X3 owners who are hitting the same problem - but would be happy to use an "outdated" phone if it meant optimal reception/transmission.
Thanks again