I use ntlworld.
As part of the 10 quid per month for unlimited access you also get 10 quid worth of phone calls (at ntl rates).
They charge a 3.5p connection fee per call but their per minute rates are about 1 p less than BT. Also those rates are for local AND national calls.
About the only downside is that they cut you off after 2 hours of use. You can redial of course, but it's a bit of pain if you're 90% of the way through downloading a file.
One other slight niggle, but I don't know if it's them or my setup: Often it takes a 30 secs to a minute or so before a new page begins to be loaded after clicking on the link.
Usually manage to log on 1st time. Nearly always get a connection at 45k, fastest was a shade under 50 k.