BT recently released a new website (
http://www.switchedonuk.org/) which
tells you when your exchange is likely to be upgraded to BT's new network.
(Samknows has also converted these dates to an approximate map of the UK at
http://www.samknows.com/broadband/images/21cn.png)
They also have
http://www.btplc.com/21CN/index.htm which gives further
information on the upgrades.
Its interesting to note that while most parts of the country will have the
entire exchange upgraded at once (and where the process has already started
around Cardiff), other parts of the UK (mainly major cities) will have the
broadband element of the exchange upgraded first between now and 2008, so
that BT Wholesale can introduce ADSL2+ based services (probably) at the
beginning of 2008 to (initially) around 50% of the population.
Regards
Sunil