hsg@h-gee.co.uk declared for all the world to hear...
> Would a cloned SIM run the car phone while the real sim is used in the original
> Nokia mobile?

If you could successfully do it, which you can't without destroying the
original, yes.

> Would both phones ring?

NoIt's likely that neither phone would ring.

> Would T-Mobile know?

Yes. And would almost certainly cut you off.

> Anybody done it?

Not that I know of.

> Where do I get a clone SIM card?

CLining only worked on very very old SIMs. With a modern SIM you have
more chance of winning the lottery.
--
Regards
Jon