no soda machines, that's what room service and bar service is for. You can get a soda from the bar and bring it back to your room at any time or you can order a soda from room service at any time.
When you get on board, buy a soda card. They usually run about $22.00. They're good for unlimited soda. Some people said you couldn't use them in the resturants, but I had no problem using it on the Grand Princess last year. It's worth it if you drink a lot of soda. On a 7 day cruise, I can do that!!
You can definately use the soda card in the restaurants and everywhere else for that matter with the exception of Princess Cays since there is no fountain soda service on the private island