Deactivating iMessage on an iPhone
Deactivate
iMessage
Complete these steps from your
iPhone before starting to use your new Android device
1. Launch Settings from the
Home screen of your iPhone.
2. Tap Messages.
3. Tap the slider next to
iMessage to turn it off.

4. Go
back to Settings.
5. Tap
on Facetime.
6. Tap
the slider next to Facetime to turn it off.

7. Now
hop into the Messages app and send some messages to people you know have
iPhones to make sure they can message
you back. You want green messages bubbles for everything.
Once you're done this, iMessage
should deactivate from Apple's servers
and you shouldn't have any issues, nor should you have to go any further into
this guide. As a side note, the sooner you do this, the better off you are. If
you know you're going out to purchase an Android, BlackBerry, or Windows Phone
in 3 days, do this process right now. That way you have turned off
iMessage and it gives the servers a few days to actually process
the request completely and boot you off.
Once you've switched to your new smartphone, verify you can send and
receive text messages to someone else using an iPhone.