Can I move home phone to PlusNet before my 12mth pre pay with BT expires

[#1]

Hi,
We are on 12mths pre-pay rental with BT which will expire near the end of November. However, I would like to move my phone to PlusNet (where our broadband is) and pay 12mths rental in advance at the lower prices before they rise on 18th November.
So can I sign up now in October at the current lower price for 12mths rental and move from BT straight away?  Or even better have the actual switch over when the BT pre pay expires and they switch me back to standard billing.
Cheers..

[#2]

I believe you can leave BT straight away, but you wont get any refund from them.

[#3]

Well I put the move in place back on Nov 6th so with the promised 7 to 10 day time to transfer it would be done before my billing date with BT and the expiry of my prepay 12mth line rental saver.
What happened?  Well PlusNet systems screwed up and did not place the request to transfer. So now I am past my BT line rental saver renewal, onto the next month of calls and line rental with BT and now waiting for the promised transfer to PlusNet on the 7 December ( over 1 month and over 2 weeks late).
No offer of compensation for the extra cost that the mistake by PlusNet will cost us on rental charges.  Only compensation is that my order did go in and get paid for on the 6th November so at least it was at the pre increase rate.
Not good for what is supposed to be the supplier with the best customer service .  Hate to think what the others do..