iPhones are nice but using the ExpoDev software on a Palm phone is much more functional.
Of course you need to do some calibration but for about $50 you can have the view camera store do the densitometer work and enter it into the Plotter software and email you the file for the Palm phone.
I enter the EV high and EV low values along with my Zone placements, desired f-stop and the software determines the exposure time, calculates reciprocity failure, deals with filter factors and bellows extension factors. It has a built in timer for multi-second exposures that works well. It allows for written notes about exposures and keeps track of film and lens focal length. It determines development time for each sheet of film and stores the information in a Microsoft Outlook memo that automatically syncs with my computer. The software works with both spot meters and incident meters. They have a large number of built in film-developer data that you can use if you don't want to do your own testing.
On my phone, I can also take a digital photo or video of the scene I am photographing and make voice memos.
I don't think the medley of deconstructed iPhone applications can compare to this.