If you read their website, line rental is £11 - you pay it to them rather than to BT.
Therefore cost is £20.99 + £11, but you are paying £11 to BT anyway...
It works by using LLU - local loop unbundling - where CW will 'own' the line from the exchange to your house. About 70% of the UK is eligible (about 90% of existing customers).
Not in my village though
Check carefully, as TalkTalk receive loads of criticism. One thing I wonder though, is that TalkTalk use 'packet shaping' to throttle P2P etc at peak times. The new service is a 40 GB cap, so will they stop doing this?????