I don't recall do both AT&T and Apple iPhone deliveries require signature on delivery?
I have not had to sign for my phones the past few years (all of them ordered from AT&T). Even if it does require a signature, you can print out a form for them to deliver it without you needing to worry about being there to sign it. Or you can request that they leave it with your neighbor (if you have one and/or trust them to hang onto it for you).