persistence based on MSISDN number

One way to accomplish this is with the universal persistence profile, which lets you persist on strings located within, among other things, HTTP headers. For example (and I'm getting this right out of the book I received in training):

 
 when HTTP_REQUEST { 
   persist uie [findstr [HTTP::URI] "user=" 5 "&"] 
 } 
 

...will persist on a name/value pair as presented in the URL string. There are probably other ways of doing this, but this came to mind immediately.