Sending single SMS message to multiple contacts causes MMS
This is an easy problem to fix, I believe @BryanDenny already mentioned it. 


Go to the stock Android messaging app.
Click the Overflow menu button down in the lower left hand corner (it looks like three boxes stacked on each other).
Select "Settings" from the pop-up menu; should be the first option. 
Under "Multimedia (MMS) Messages, uncheck the item that says: "Group messaging- Use MMS to send a single message when there are multiple recipients".