We saw some long lines at the kiosks a couple of weeks ago at MK and EPCOT. Might be worth taking your phone just to avoid the aggravation of having to line up to check your times.
In the event you need to change a FP because you're stuck in line for another ride may make it worth carrying your phone. I know I don't want to stand in line to a kiosk, I'd rather the in line for a ride.