I started an earlier thread which closed when I (thought) I had the whole
answer - thanks to those who contributed.

I've a 2002 C220 CDi with the car kit for Nokia 6310(i) fitted.  I have a
more modern handset that I prefer to use, but also have a 6310 that works
fine in the Mercedes fitted kit.  For obvious reasons I don't want to change
the kit in the car but also want to use my more modern handset for general
roaming.  I've been told that the UK cellular operators offer a dual/twin
SIM which addresses this problem e.g. 2 different phones can have the same
number (without constantly messing around and swapping SIMs, resetting time
etc).  That way I can use the modern handset for general use whilst keeping
the 6310 for use with the car.  Does anyone have experience of this?  Do
all/some/none of the service providers offer this?

Thanks for your help

Steve