That's a tough one BG, The Minimum I can find is 12 Months too.

What about Speaking to your current service provider and asking if they could do you some sort of deal.

Could consider pay as you go on dial up. Depends how much you intend to use it but it may be a cheaper option.

Virgin broadband does no fixed term contract, but there might be a caveat from BT on the installation of the line. I had a quick look at the Virgin site but couldn't instantly find a package that included home phone calls, but it might be worth further exploration, as it is unlikely that they would miss out on one telecomms service when they offer so many others.

I believe Nildram offer monthly contracts using bt lines.

If you need enter a contract with bt for line rental it may be for twelve months
but this can carry on when you move
to your new home.

This may only be an issue if you decide
to switch to cable.

best to check with bt on that,