In message , at 15:01:49 on Fri, 16 Mar
2012, MatSav remarked:
That has been alleged to have happened on English south coast
shores/beaches which are screened from the local transmitter by
high
cliffs but within range of French base stations.

Sometimes, exceptional atmospheric conditions can cause this from
elevated inland points as well.

I was at the Great Dorset Steam Fair http://www.gdsf.co.uk at
Tarrant Hinton, and made some calls to friends who were elsewhere
on the very large fair site. When I got the bill, I discovered I
had apparently made calls in France *and* the UK within a few
seconds of each other.

The mobile phone systems utilise a transmission protocol known as
TDMA (Time Division Multiple Access). In theory, this should
block connections where the propogation delay is more than 28
milliseconds (equating to a distance of about 90km). In my case,
the nearest point of the French coast was at least 130km away -
so it shouldn't have been possible, but it definitely happened.

Coastal base stations (such as the one which you contacted in northern
France) can be adjusted to allow twice the normal propagation delay, so
that large areas of sea are covered.
--
Roland Perry