It’s been allowed everywhere I have ever lived in the US.

The issues you’ll run into is they get all stupid about it if your service ever goes down. They’ll always blame your router/modem first. (Literally the entire neighborhood could be down and they’ll act like it’s something specific to your device). Sometimes they try to charge an install fee or a connection fee or other dumb shit.

I think their are local laws that require them to allow byod too. It depends on your area though.