we do not have smartphones. yes - medallion will come in the mail before you leave. you will use it to enter your room and that is about all. oh, you can use it in shops to buy things, or when you go get specialty coffees/drinks etc you will show them your medallion. even if you have the drink package you will show your medallion to the bar tender.
you will have the princess events list which is the old patter on your bed each night. you also can use the television in your room to view various things.
use your computer at home to register - princess now has a web option, to do this. you can also set up dining times at different dining rooms, book excursions, etc.
so - if you have a medallion and smartphone you can order food/drink anywhere on the ship and they will deliver it to you.
but, like i said above, a smartphone is not needed. the medallion is identification leaving/entering the ship, buying things on the ship, opening your room. you should wear it or keep it in your pocket while on your cruise. if you go ashore, also take it with you, to use to get back onboard.