Hangouts and Google Voice use data (WiFi or Mobile Data.) SMS uses the voice stream. MMS uses WiFi and data. I remember in versions of Android past that the number of texts sent and received within a 5 min period might get halted until you acknowledged a pop up notice on the screen referring to "You have exceeded x-# messages in x-# minutes." It was a way for limited text plans to keep an eye out for runaway texting apps. I myself, am able to send and receive in almost rapid fire succession. I use the stock app on my phone through CDMA. I used to use Hangouts, but since I don't use data, I can no longer.
Have never seen the pop up but the behavior is very much, that system is
still intact and influential. I have unlimited.
Just because you don't subscribe to data does not mean you cannot use WiFi.
However, my plan offers a tiny 500MB portion. Less I am on a job site with
spotty reception, and poor WiFi or worse, I rarely ever burn out my data.
95% of everything I do is over WiFi.
Don't become dependent on any one service. But learn to use the Duality of
the Cell services and WiFi as there will be times that one or the other
will not work very well. Don't limit yourself if you don't have to.