all 8mb dsl services are dodgy as atm. bt are having issues which have been going on for a couple of months now.
I use nildram (now owned by pipex) and while I occasionally get issues I've found their CS awesome.
However it's not cheap (is quality ever cheap?)
I pay just under £30 per month which gives me 50gb per month (any left extra rolls over to the next month) at whatever rate BT can handle... in the mornings it's usually about 5.5mb and the afternoons it slows to about 2.5 - 3.5mb. Should be noted I pay a little extra to get a static IP.
As for premium or national rate numbers... take a look @
SAYNOTO0870.COM - Non-Geographical Alternative Telephone Numbers