POTS and PSTN will still be around for some time in the UK as the BT 21CN can't really cope with reliable IP based VOIP traffic, the multi billion investment by BT for its 21st century backbone network infrastructure is being constructed using cheap Chinese made routers etc (rather than purchasing British made nationally more secure Marconi kit), which has high latency and packet loss problems. The move to an IP based telephony, for BT landline and Virgin Media (the telephone is still using POTS/PSTN rather than a cable modem), which was promised a few year ago is doomed to failure. The network isn't even IPv6 capable.

http://www.theregister.co.uk/2008/10/10/21cn_ipv6/

http://www.theregister.co.uk/2010/07/01/aa_bt/

Best to stick with the 50 Mbit/sec Broadband line from Virgin Media (the 100Mbit/sec is a little spendy for not really much performance difference). I do even though I can get free BT ADSL Broadband as going back to 3-5 Mbit/sec is really a no brainer.