You may have used the term "Text message" interchangeably when using SMS and MSM. However, they are different technologies used to send messages over a cellular network.
SMS = Short Message Service
MMS = Multimedia Messaging Service
SMS message contains only text (no pictures or videos) and is limited to 160 characters.
Whenever you send a text with an attached file, like a picture or video, it uses MMS - It is limited to 1,600 characters.
Nowadays, almost all phone devices support both, SMS and MMS, so you don’t need to pick one over the other. Any message over the maximum size or that includes multimedia, will automatically be sent using MMS.