Default Sent text shows up foreign characters on others phones

OK, so My wife has the S5 - Tmobile version, but posting here hoping for additional crowd help.

She was running stock, NO ROOT, and when she sent text messages to some people, they would show up as blank boxes on the other person's phone.

Then, after a factory reset, today she is saying certain people she texts(different from above problem) are saying the texts come through, but look like Chinese characters.

Not sure what to do. Is it a carrier's problem? Is it a phone problem?

HELP, she is frustrated...