I still have an old Motorola pager of this type. Not used it for a long time, and forgot that I had been informed (as another review in this series says) that the code has been changed to 07623 (from the old 01523). I have just tested it - phoned the number, and asked them to send me a message. It works!
I am not planning to sell it, as it's a good back-up to a mobile phone, is small and neat, and is cost-free apart from an AAA battery that lasts for ages. (Caller pays approx. 50p). My internet researches suggest that new subscribers may have to take out a monthly contract, though: I'll wait and see if my new use of it brings a contract demand!
UPDATE April 2008: It still works fine, and I have had no payment demand. I am glad I kept it.