Just to balance the last company recommendation, a company warning. BT don't even do the little they say they will.
Last September, I finally escaped from BT's shoddy telephone service to a 12-month contract with 'it' http://www.itplc.com/ - they're OK, but probably not the best or cheapest that you can find now. I wrote and told BT exactly why they lost my account (basically, bad customer service habits, combined with only offering "bundled calls" packages so other calls providers are less attractive). I got an amazingly stupid typed reply explaining why BT's brilliant. Not a good answer. Like I'm going to read a sales pitch and thing "yeah, I imagined all those problems moving house, getting my business number, and so on."
In April, I had a letter from BT inviting me back with the first headline being "Enjoy low prices on all BT Together call options" - "Together" being the package that I was moved to and quit. I called the number on the sheet, asked to be removed from the "come back" mailing list and was assured it would be done.
Today, another letter from BT, now offering a "Special Offer" if I take one of their bundled calls packages. Amazing. The absolute clincher is that the letter finishes with an advert for "BT Privacy"! Not privacy from BT sales letters, I guess. Could these people organise a brewery event? Again called, again assured, and this time asked them to send confirmation in writing. Is it worth taking this further? I'm not sure.
In my opinion, anyone staying with BT should have a really good motive. There are many other line renters nationwide now, including phonecoop.
Hope your telephone behaves better,