Question Is Switching Plans as Simple as Switching SIMs in GSM Phones

[downplay]

I have Verizon prepaid with my unlocked Apple Xs Max. I see a great deal I’d like to use on AT&T.

BUT, they demand that I buy one of their phones. It should still be worth it if I can just switch out SIMs because the cheapest phone they have is only $59. Can I just buy their phone with their plan, take out the SIM, put it in my Apple, and be set?

Would the only side-effect be having a new/different phone number?

 

[hang-the-9]

Not sure why you need to buy their phone, there is a bring your own phone option https://www.att.com/wireless/byod/