I'm looking for a DECT phone which can handle two outgoing phone
lines.  The only one I can find is a Siemens Gigaset 2420, an American
model.

I live in the UK, and use both BT & Telewest phone lines.  What I want
to know is:

(1.) Will the American Gigaset work with the UK phone system (I know
it has to be BABT approved to be legally usable - but that's my
concern ;) ).  I've seen modems that have adaptors to use the BT RJ11
plugs, so i presume i could just use one of those, and a 110->220
transformer for the power.

(2.) Will caller ID work on the Gigaset - is caller ID done
differently on US networks to UK ?

Hi:

I am not an expert on this subject, but I know enough to at least give
you a little information. European cellphones use a system called GSM,
which is a digital cellular phone system. The U.S. is still using
primarily an analog system (the name of which I don't recall at the
moment and it's not that important in this context). Although we do
have digital phones, the cellular system we actually use is still
primarily analog. Because the U.S. system was developed first, we now
have to backtrack to 'digitize' ourselves, whereas  countries in
Europe and elsewhere did not start widely using cellphones until it
was possible to build a digital network. There are some GSM phones
sold within the U.S., which can then be used in Europe and other
countries, but they are very expensive and not widely available. The
key thing you need to remember in buying your phone is to ask whether
or not it is a GSM phone. If it is, then it should work in the UK. I
hope this helps.

Oh, for heaven's sake. I just realized that your question had
*nothing* to do with cellphones, but landline phones. Now I have a
very red face! <g>

I do have something I'd like to point out, though, about your using a
US electrical product in the UK. Long-term use of an electrical
converter can be a problem. A 220-volt electrical line generates quite
a bit more heat than a 110-volt line. The converter, as a result,
becomes quite hot. I've actually melted more than one myself when
leaving an item plugged in for more than a few hours. If you're going
to use a phone, I can see that this could be a serious problem. I
think you'd be much better off finding a product that is internally
wired to handle a 220-volt power supply.

Yes, the phone should work, given a suitable line adaptor.

The UK and US Caller-ID systems are different. It almost certainly
won't work.

I'm not certain, but I think that the DECT frequencies used in the US
differ from those used in Europe. So it won't work with other DECT
handsets here, and you may (I don't know the licencing status of the
bands used in the US here) have the Radio Authority descend from on
high all perturbed.

I reckon your best bet would be to ask the good people in uk.telecom.
Someone will have an exact answer, and someone else may be able to
point you in the direction of an equivalent UK product.

dmsvoltaire might like to know that the UK (and Europe) had extensive
analogue cellular networks.

FWIW, during my time in retail electronics here in Canada I sold
numerous cordless phones which were to end up in Europe and the U.K. 
All that was necessary, aside from legal issues, was to 1) replace the
power adaptor with a european model and 2) purchase an adaptor for the
modular line cord.  I had enough repeat customers (UK, Germany,
Iceland) to be confident that this works.

I can't advise you about the Caller ID issue, unfortunately, but if I
can turn up definitive info I'll post an answer.

This DECT phone will work in the UK. I have brought US phones to the
US and used them with 100% success. You need to buy a US to BT style
phone jack adapter which you will find on the web. If you can't find
one then buy the BT style plug at B&Q, remove the US phone line plug
and fit the BT type. The red and green wires in the phone line cable
go the center two wires of the BT plug. Polarity is not critical. The
phone will ring correctly and will work without any problems. The DECT
transmissions however are not on a UK allocation and that maybe an
issue at customs when you import it.

You say this a US 2 line phone and therfore may have just one phone
line cable coming out of the phone. The answer here is that the red
and green wires are line 1 and the yellow and black wires are line 2.
In the UK this will not work into a single BT socket so you will have
to solder a flying lead to each pair and fit a BT style plug on each
of the flying leads. Plug each of the flying leads into your two BT
lines.

By the way I have also taken UK phones and used them in the US. That
is not so easy as UK phones are wired in a way that requires you make
up a small conversion box between the phone and the incoming line or
the phone will not ring!