Android phones and iPhones use non standard messaging protocols on top of their sms (texting) applications. On android it’s pretty invisible to the user. On iOS it uses a blue speech bubble for the text to indicate it’s an iMessage (apples sms extension) instead of a green one. I don’t know why normal people care, but both companies have been trying to get the other to use their standard for years now.

Iirc apple had it before google but they weren’t the first (blackberry might not even have been the first).