A third source that seems to refute this hoax is
the BBC, who quote the Wiltshire Police Force / ICTIS as saying that it's a hoax.
As a techie (although not a telephone system expert), I cannot think that it is possible these days for a line to be 'held open' by the call initiator when the recipient of the call has terminated the call. ISTR that in the old days of mechanical Strowger exchanges, there were ways that the line could be captured and 'held' if the originator didn't replace the receiver correctly, but I've never come across an instance of this in one of the System X (digital) exchanges.