Actually you mention something thats kind of important. Probably for another thread, but maybe you can help.
My daughter traded in her iPhone for the Galaxy over a month ago. She still has a few friends who cannot send her texts, they send them she never receives them. She has contacted both apple and at&t and neither has been much help.
What solution has worked for your contacts to successfully send you messages?
Basically I did 2 things: I removed my iphone profile from my Apple ID, and Then her friends have to highlight the text before they send (hold finger on the text where it shows as they are typing it), until the option pops up to "send as text message" once they do that, she should be fine.
The problem it seemed was that she still has an Apple ID associated with the iphone and her friends devices still recognize that address. It solved my problem when they sent the text "as text" and not "imessage".