It would take away competition between the cariers -- Ofcom wouldn't
allow it.

As you know UK SIMs used in UK will not roam to the other 3 carriers,
whether or not handset is locked, but abroad will use best signal.

So, if cost not important, but always having signal is [country
doctor, even road rep selling high value], then it would make sense,
would it not, to get a French, Irish, Dutch etc phone & contract, and
over here it would roam all four networks at will. Even if talk was
£50 an hour more than local tariffs, that could easily be worthwhile

Do the emergency and security services and cabinwt ministers and the
like have special SIMs/contracts that roam as I have suggested? Why
don't the carriers sell such contracts, they cross-settle airtime mins/
bytes anyway.

Dave

They should roam for emergency service purposes.

There was a company offering SIM's from Liechtenstein.

Not cheap for outbound (but reasonable) and incoming involves an
international call and it will roam on 4/5 networks in the UK (all the GSM
ones).

I don't need one where I live, but if I were a vet in the Scottish Highlands
then I would have one and a proper (high power) built in car phone to put it
in.  Then if you do manage to slide off the road into a ditch in the middle
of nowhere and a snow drift starts building up outside you have a fairly
good chance of being able to summon help.