My impression from the terms and conditions is that you cannot leave your current contract without penalty. If there is a change in the terms/conditions you can, but price changes are not covered by the terms/conditions. Interestingly, there is a clause for mobile plans where it explicitly says you can leave if there is a price increase, but nowhere that I can see for phone/broadband. I may be wrong, but the T&C's are not that clear on the matter. And, besides, even if it was possible, I imagine it may turn into a nightmare trying to leave without penalty if their normal customer services standards are obeyed
Seems a bit silly to move for this reason - for ages now, TalkTalk have always copied BT's line rental and call charge increases (usually around 1 month after BT increase their prices), and that is all these latest changes are. So, if you are planning to avoid BT and TalkTalk, your choices are pretty restricted.