Text can be "typed" in to the phone using the number pad and stored in the phone. When the message is completely typed in, it can be sent to other cell phones using the "Send" button, just like you were making a regular call.

SMS messages can also be sent as emails to the cell phone provider and they will route it to your cell phone.

There are some limitations. For example, some SMS systems are "proprietary" and can only send messages to other phones on the same network.

Plans vary, but SMS is usually an extra charge. Perhaps charged by the number of characters or perhaps a monthly fee provides a relatively large number of characters, with extra charges being applied if you exceed that monthly limit.

But, being able to send text messages can be a huge advantage for people who can not hear well.