Here is my take, based on extensive off road adventures in areas with little or no cell coverage.
1. 3g/4g apple devices work on aGPS (Assisted GPS), and rely heavily on assistance from cell towers. Mostly, they will work out of cell range but its hit or miss and it can take 20-30 minutes to update (and from first hand experience sometimes they never update). If your going to be in areas of good/fair cell coverage then you do not need an external GPS device, however the minute your off the cell grid your going to wish you had one.
2. There are ton of GPS options. My favorite is the Bad Elf GPS pro - its Bluetooth and it will connect up to 5 devices ($130-150 bucks). Use it with an old iPad mounted in your vehicle when driving and with a phone when you go overland by foot - its a real champ! (about $150 from online resellers such as eBay.)
3. Software/aps There are a ton of options, and again it falls to your needs. My favorite is GAIA Pro ($29.00), GAIA has a large selection of map types and layers and you can toggle between the layers (google, USGS topos, Road maps et). It makes it very easy to move from hard top to backcountry and navigate both on foot or vehicle. The important thing to remember is if your off the grid, your programs are only as good as the maps you downloaded to your device before you go off grid and maps eat space. With GAIA, you can pick your regions and map types so it gives a high degree of flexibility.
A few other things to keep in mind if your seriously going remote.
1) Anything with a battery, or moving parts can and will fail. I recommend that your carry a back up hand held GPS - Garmin or the like.
2) Old school is still the most important school. I also carry a compass and paper maps (topo 1:24,000), you can download topos from the USGS, pick them up at your local gear spot or order them directly online. The key is having some idea where you are and the direction your heading at all times. You'd be amazed how many people run with GPS and have no idea where the are. The second GPS is gone, they are lost lost lost. At the very least you should have an exit strategy -i.e. the hard top is 20 miles east of my position - in a pinch you work your way east with a compass....et.
Good luck and high adventure to you brohiem!
