There is known issues with ANY phone when coming from iPhone and imessage. Other people's iPhone still thinks your using imessage.
If you still have tour iPhone, go to settings, turn off imessage and get a few pals to send sms to see if they come through. Ask them if their bubble colour on their sms is green or blue (green been normal sms, blue been imessage). If it's green hopefully that will be sorted.