Around here, the term "survival cellphone" is a bit of a misnomer. With the high local mountains and only a few major corridors (roads, highways) that traverse them, coverage is very spotty even in the metro area. Here you can be on a mountain and within visual sight of a city and not have any cell coverage. The local SAR is always telling people that you cannot depend on a cell to save your life in these parts.
Once you get out of the metro area, cell coverage is next to none. On our trip this past weekend, there was no cell coverage for well over a hundred miles, and this is on a major highway. In these areas, whether you are driving or out hiking in these areas and run into trouble, then you might as well be on the moon as help will not be forthcoming anytime soon. It is for these reasons that I always carry a PLB and also looking at the new SPOT 2 for daily message comms. The soon to be released
Delorme inReach that DR posted info on, also looks promisinng.
Regardless with the above in mind, I always carry a cell (Android based) with an extra battery along with a wall charger, car charger and also a USB cable that allows the batteries to be charged just about anywhere because as much as I like it, my cellphone is heavy on the battery usage.
Another nice feature and not directly survival related, the phone allows our laptops to be tethered when there is no internet connection, but there is cell service. Although not as fast as broadband connection, it is still much faster then dial-up.
As for installed apps, there is Google Maps, Google Earth,
Google My Tracks along with several offline saved maps of the area(s) we would be visiting/hiking etc. Several different GPS programs, first aid manual, the SAS survival manual in pdf format etc.
Although I don't own an Iphone,
this website I frequent has a good collection of outdoor related apps.