ATT go-phone nano-sim in Lumia Icon questions

I've read the Lumia Icon can take an ATT nano-sim and work fine except for LTE (it'll still get HSPA+, which I'm fine with).

1.Would there be any confusion if I put a go-phone nano-sim in?
2.Would I have to pay an activation fee?
3.Can I swap the nano-sim back into my old phone with ease?
4.Is there anything unusual I should know about using a Verizon phone on ATT?

Thanks!

PS: Any additional information/ would be great!