BT has launched a downloadable VOIP guide for businesses. Their "understanding VOIP" guide is free to download, but I found it annoying that you have to fill in your details before you could get that. (So BT sales can bombard you with calls/emails?)
Anyway, if you are interested, it is here.
Understanding VOIP | Downloads | Small & medium business | BT.com
I have not downloaded it myself yet, so unsure if it is useful for home users.