I have an iPad with a built in GPS, the Garmin App and the Bluechart of Eastern North America to Trinidad with the Active Captain overlay. I've also got a Raymarine chartplotter which uses Navionics and a computer with Maptech. The iPad is an excellent plotter and in conjunction with paper charts I wouldn't hesitate to have it to use in an area in which I sailed exclusively. I believe that smart phones can use the same app but I don't know whether they also have built in GPS receivers.
I use my Raymarine to make my routes and it's tethered to my autopilot. I use that for navigation. The Maptech as a back-up and the iPad for detail.
All smart phones here in the US have built in GPS functions, it is something that the government mandated after 911, and it was on most prior to that time. Not sure what apps are out there for ocean navigating, and since I cannot see the screen on a phone as well as some people can outdoors, I have to wear very dark sunglasses to keep my eyes from hurting a lot, I would not be able to use it as well as an ipad or the Verizon or blackberry tablets.
I have my laptop, my tablet, and I will have a good networking chartplotter tied in as well. Since in order for me to afford to sail I would have to have email and occasional internet access I am going to have to have the computers anyway, and I am comfortable using the tech, so the paper is not really something I would want, other than guides. Even the guides I buy are for the most part ebooks, which I store on multiple systems. I also back up to an internet site, in case I lose one or more systems, that way I can pull out a spare computer from a waterproof case and hook it up and reload everything if I have a serious hardware issue.
Even paper charts will take a bit of damage if you dunk them in saltwater and leave them there for a bit. Even laminated one, especially if you use them a lot, will get ruined, the water comes in under the worn edges. I guess the paper is the only way guys have them all stored in sealed rolls, and have backups in other sealed rolls, that way they are just like me, covering their butt for when the problem happens.