I just wanted to share my experience with 4tel, with whom I've recently taken out a contract for my business telephone.
4tel have been helpful, friendly, polite and efficient.
All their support phone numbers are free 0800 numbers.
Their prices are very reasonable, much more so than BT. They aren't the cheapest, but I believe you get what you pay for, which leads me on to....
Their customer service is excellent - they phone you back promptly and know what they are talking about. Error on the line? No problem - BT were there within the day to fix it.
Broadband activation on the new line was very quick.
It's all too often we hear about negative customer service, especially from utility companies, so I wanted to post something postitive for a change.