How to Remove My Mobile Number From Yahoo IM
The popular Yahoo! Messenger instant messaging program allows you to register your mobile phone so you can receive instant messages, appointments and other Yahoo notifications as text alerts. If you find the messages distracting, unregister your phone to stop receiving the alerts. You may also want to delete your phone from your Yahoo account if you lose it to prevent someone else from viewing your alerts.
Open Yahoo! Messenger and click the "Messenger" menu option.
Select "Preferences" from the drop-down menu.
Select "General," which is the first entry in the left window pane.
Click the "Edit Mobile Phone" button at the bottom of the window.
Click the "Delete" icon next to the number you want to delete. A new window will open where you can cancel any alerts associated with the number or forward them to another device. Make your selection and click "Delete Device."