Can you use an iPhone for any carrier?

I'm paying off my 7 plus to get a new phone. And I planned on giving this phone to my brother, but he has cricket and I have Verizon. So I'm wondering if he'll be able to use it with them?

Yes, that should work. Almost all Verizon smartphones are GSM unlocked. So in theory, you would simply take out the Verizon SIM and put in your brother's Cricket SIM card. The phone should detect it and restart and it should accept it.