yeppers....many have had a not so good surprise after cruising when they got their cell phone bill for certain !
My advice..... turn it off when you get on the ship and do not turn it on until you get back ! Even if you leave it on and do not answer the phone and someone leaves a voicemail... the bill will be astounding !
Some carriers offer international plans for a prorated duration while you are on a cruise and you could use the phone when in a port of call and off the ship....check with your carrier for options.
As for the Ipad..... well for me, I am going away to get away from those devices, but those that insist on using them can also incur a hefty bill. Cheapest way to access the internet is at a "Cafe" in a port where the charges are minimal compared to what the cruiseline charges !