Talk Talk plans to move Tiscali Customers over to the TT Network.

"We’ve been single-minded in our determination to maintain and enhance your current service. For the time being, you’ll stay on the Tiscali network with your email address, your billing information and your customer service numbers all remaining the same.
So what’s changing? We’re planning to move Tiscali customers on to the TalkTalk network as soon as possible so you can enjoy its full benefits as a TalkTalk customer. The good news is that TalkTalk’s Next Generation Network is the biggest in Britain with 90% of customers who move to us saying that they prefer it to their previous provider.
You’ll also see that we’re committed to delivering faster and more consistent speeds and the very best value, such as free calls to 0845/0870 numbers and to four million fellow TalkTalk customers.
At the moment we’re concentrating our efforts on improving the service you receive and, in the coming months, we’ll be in touch with some bright ideas to help you enjoy your phone and broadband to the full.
However, if after hearing all this you want to join us straightaway, simply call 0800 049 1412 for a fast track upgrade."

http://www.tiscali.co.uk/members/talktalk-july-09-update.html?lpos=content-slider-1-1&lid=content-slider-1_wevejoinedforceswithtalktalk