Originally Posted by
jp1
Are you trying to send them to another iphone or to an android phone. To another iphone (or ipad) (blue messages) it should send them over wifi because it's using the iMessage system. If to an android (green messages) I'm not 100% sure but I believe that it sends them over cellular since those are just old school SMS and MMS text messages.
Also, depending on what carrier you have you may be able to enable wifi calling. I believe if you do that you can then send SMS and MMS messages (texts to non-iOS devices) over wifi.