In the past, Apple has continued to force iPhone users to stick to Apple products, making it difficult to move to Android even if they wanted to. One of the biggest ways they did this was through iMessage: until earlier this week, it wasn't possible to get your phone number out of the iMessage system, even if you changed to Android.
What this meant was that iPhone-turned-Android users would not get text messages from other iPhone users, because their numbers would still be registered to the iMessage system, so Apple would try to send the message via iMessage, and it would get lost to a space that Apple created. And there was no easy fix.
Now, however, users can go here (https://selfsolve.apple.com/deregister-imessage) to deregister their number from iMessage, and the problem is solved.
Awesome, Apple, great. Still, you have known about this problem since 2011, so this solution is incredibly late. So, now, if you're thinking about making the switch, make sure to check out Google's guildelines for making it easy! (http://www.android.com/switch/)