Sorry to resurrect an old thread, but something useful to UK VoIP users who would rather not be paying for the POTS line - Primus have slashed their cheapest line rental offering to £5.99/month - it's called Line Rental Saver and only available through Broadband Choices.
http://www.broadbandchoices.co.uk/of...s/primus-phone
I don't work for them - just a happy customer.