So, I kept sending two messages from my iPhone, one was SMS, and the other was iMessage (to iPhone users). After countless web searches, forums searches and online help desks, which never got me anywhere, I finally figured out how to stop it.

Step One:
Settings:

Step Two:
Send & Receive

Step Three:
“you can be reached by iMessage at:”

“start new conversations from:” will go away when only one of the above settings are check marked.

Step Four:
uncheck all except the one that is tied to your iCloud account so that you can read all your messages from any device that is connected to that iCloud account 🙂

Step Five:
test it and see what happens.

Let me know if these instructions were helpful to you!