A:AnswerIt's a setting. Go to settings /messages/ send and receive. Make sure "start new conversation" has your iPhone phone number with a check mark next to it. BTW, you can Google this kind of stuff. I've been a Apple guy since the eighties and I still use Google for lots of answers.
A:AnswerIf it’s any of the newer iPads they no longer use a physical SIM card. They now call it E- SIM. It has to be connected to an email address in order to get the info in it.