Thanks for all the replies.
FlyingFemme has given the best answer to my question, ie:
Iridium handheld 9505, plus car antenna on 'dash', connected through simple interface (VL1000J comes in at about USD250 but amplifies and cleans sound apparently) works fine.
SNS3, whilst I thank you for your efforts, you have slightly missed the point of my question - unless you are using a handheld unit, with simple direct to headset interface, but I don't think you are??!!
I'm off to choose between USD30 or USD275!
I'll let you know how I get on!
Sam.