New customers will get the price rises straight away. Prices for existing customers will rise from 1 May:

Standard line rental will increase from £15.40 to £15.95. 
SimplyBroadband package price will increase from £2.50 to £3.50. 
Essentials TV package price will increase from £7.50 to £8.50. 
Plus TV package price will increase from £15.50 to £18.50.
Essentials package price will increase from £7.50 to £8.50. 
A number of TalkTalk's old packages will also rise by between £1 and £1.40. See the TalkTalk website for full details.

From 1 June, the standard rate for calling UK landlines will rise from 9p/minute to 11.5p/minute. 

TalkTalk's Value line rental will also rise from 29 April for new customers. The upfront payment will increase from £126/year (equivalent of £10.50/month) to £141/year (equivalent of £11.75/month).

http://sales.talktalk.co.uk/pricing/info/pricing-notification

Talk Talk say you can leave penalty free  if you tell them up to 30 days after you recieve your official notification.