BT used to be the monopoly provider of telephone services, from GPO to British Telecom with the yellow Ital vans.
(Apart from Hull, which is an anomoly in more ways than one
)They own the boxes and lines (apart from NTL/Virgin Medias, Hull and Mercurys).
They have to allow other broadband and call providers to use their lines (a bit like Royal Mail have to let other companies post using their post), so they set up BT Outreach to enable this.
The 3rd party company will use their own switches but most of the lines will be BTs.
They seem to perform almost under protest, they can be *very* slow at setting up 3rd party lines.
