How much do people pay attention to that detail, though? I certainly haven't. And I at least differentiate between UPS and USPS while I know a good handful of people that don't remember which is which and don't particularly care.

Plus, if you're buying something on Amazon, you have no idea who will be shipping it when they ask for the shipping address, so pretty good chance you did give your phone number when buying the thing you're expecting from USPS.