It only appears to be a limited time offer for new customers taking up the Talk Unlimited service and it only saves them £5 per month for a 256k service capped at 750Mb. TW 256k service is normally £17.99 if taken with another TW service, otherwise it is £19.99.
NTL have had better offers such as free base pack TV or free dial-up internet for a year when subscribing to the telephone service with Talk Unlimited and free installation. My daughter took up this offer with NTL but wanted broadband so they gave her £10 per month off for the first year.
Seems like the NTL offer was far better than the Telewest one is.
