I've been subscribing to BT Midband for best part of a month now [only avaliable on ISDN } 150 hrs anytime less pro rota the more you use the 128k connection facility. But at a tenner a month I reckon it is as good an offer you will find for the ability to connect at 128K if and when required.
No email or Webspace provided, but used in conjunction with another ISP, its the nearest you can get to Broadband until it arrives, at a price less than BT Broadband.