Recently 2 of my friends switched from apple to android but the phone still recognizes them as iPhone so they don't receive any of my texts and I can't receive their replies. And once I turn off iMessage all the people who have iMessage I don't receive

http://support.apple.com/kb/ts5185

Sorry, forgot to state. The issue isn't with your phone but with your friend's phone.

they need to log out of imessage or deactivate imessage or call apple support.

I am having the same problem with some friends of mine. They have already switched off their iMessage but my phone is still saying it's an iPhone and the problem is still unresolved even though other iPhone users have successfully sent an SMS to her with iMessage still on in their phones.

Have her try the second section listed in the article. On your iPhone delete her contact and then add it back.