How to Disable iMessage (Help!)

Hey everyone, It was time to put my iPhone 4s to rest so I purchased the Nokia Lumia 928 yesterday. I activated the phone and wiped my 4s in hopes of selling it soon. What I have found is that I'm not receiving messages from friends with iPhones. They are receiving messages from me, but their responses are not making it back to me.

Verizon tech support and Apple iPhone support both say that iMessage is likely the culprit since I can receive SMS from people who have other phones. However, neither person I've talked to could tell me how to disable iMessage without doing it from the already wiped phone.

I've used Google and Bing to search for answers, but nothing has come up helpful. The best advice I've been given so far is from the Apple iPhone support guy. He said that I need to tell all of my iPhone friends to make sure messages aren't being sent to my iMessage email address, to delete our conversation thread, and to send a new message making sure it is going to my phone number and not an email address.

I'd really like a simpler solution so I'm turning to the geniuses at The Verge. Thanks in advance for your help!