There is a easy way to stay with NTL (as you are still happy with the service) but have more phones in the house! What you can do is to buy a multi-handset DECH phone and simply plug the slave hand-set into any wall socket and it will work. you can have intercom as well.
the cheapest set i can recall is 80 quid for a quad-pack... but for better quality you might want to spend around £180+ but that is much cooler than corded phones
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when i was with NTL they didnt try to get me on another 12 month contract on house movnig but trying to charge me £50 for all the re-installation. and of course i didn't pay, simply 'do it for free or i will go somewhere else'