I registered my device on samsung.co.za just fine and AFAIR the original mybroadband article on this subject pointed to a url and not an sms number. That's not to say the sms procedure is incorrect either. ....
AFAIK The url registration is just a product registration and not a warranty registration. Did you get a reply saying your phone is now covered under Samsung's accidental damage warranty? Did you have to put in your IMEI number when registering?