Cell Phone "Caller ID" Needed

Dear Patrick Townson,

Pat,

I am writing software that communicates from one network-connected computer to another controlled by a cell phone (XHTML-M). The user logs in with just a password. Passwords are not guaranteed to be unique, so I need some sort of phone serial number or other similar number to append to the password to make it unique. Do you know of such a phone id number/string that I could access via HTTP/HTTPS?

Thanks,

Ray Burns Nantasket Software, Inc