Why aren't my text messages sending right away on my iPhone?

Episode 1535 (2:19:05)

Peter from Toronto, Ontario, Canada

Peter upgraded his iPhone to the latest version of iOS 12, and ever since then, his text messages haven't been sending right away. Leo says the first thing to do is call his carrier. There are two ways messages get sent on an iPhone, however. It's either being sent with iMessage which uses his data, or as an SMS. He's only having this problem with the built-in Messages app, and it's with everyone. Leo thinks it has to do with his wireless carrier.