I have just tried texting from my orange pay as you go phone to my NTL Landline and got the message in voice from the BT SMS System.
I dont have an SMS phone, but have caller display.
BT have a web page which explains the service and under the FAQ section gives the required settings for various phones. I would be interested to hear if anyone can get this to work to send SMS's.
The Web page is
http://www.bt.com/bttext