If you are not already logged in, then do so
Next to your listing for your phone, click "Change"
Follow the prompts to enter your new information.
-or-
Follow this path to solve ur problem. Click on messenger> prefrences> general > edit mobile device> next window will guide u further to edit ur mobile device.
------------------------------------------------offtopic--------------------------------------------
You entered someone elses number just to try and and he's getting your messages isnt it? Happened to me. My mobile wall full with my freinds PMs. Had fun though
.