The blurb at another site with a DECT/SMS say that:
*** SMS Messaging is a subscription service
That's not something many of them tell you when they sell you a DECT/SMS phone!
So do NTL offer a subscription - or can you subscribe elsewhere - or cheat it by entering the same SMS centre number as your mobile uses.
http://www.filesaveas.com/sms.html
If it let you get through to these, the rate would be appaling - 07xx can be pretty stinking!