[Serusers] subst_uri can'n work

[szj]

Hi:

      I use the following rule to add "user=phone" parameter in the 
"INVITE" request;
       if(method == "INVITE")
      {
        subst_uri('/^sip:([0-9]+)@(.*)$/sip:\1@\2;user=phone/i');
      };
       But I can't work! how should I do in order to make it?

       Thanks for your instructions and help!

       Best Regards

       Sun Zongjun