Apple Computer has created a programming environment for its iPhone through what they call the App Store. A recent check of the App Store shows three genealogy apps for the iPhone. None of these applications are free.
Since I am both PC and Mac based, I already have MobileFamilyTree, the mobile version of MacFamilyTree Software which only runs on a Macintosh. Graphically, this is a pretty impressive software program, both on the computer and on the iPhone. It is only $4.99 but you also have to purchase the Synium Software MacFamilyTree program for $49.00 making the whole package rather expensive. The program is very visually oriented but routine entries and sourcing are pretty awkward. Despite the visual interface, it is pretty difficult to find people and see how the families relate to each other. This was the first genealogy App available for the iPhone. I would suggest you try out the demo before buying either program.
I have not had a chance to see or use either of the other two iPhone programs; FamViewer from Aster Software which is pretty highly rated by its users but is $14.99 or Shrubs developed by Benoit Bousquet for $4.99 which is much less highly rated. Both programs claim to be able to read and display standard genealogy GEDCOM files. From the reviews, it appears that both programs have some issues in loading files from the PC or Mac. It is good thing to remember that these are Apple iPhone programs and therefore do not run on PCs at all.
Getting away from the trendy iPhone, you might want to check out MobileGenealogy.com for a forum on mobile genealogy. The premier program is NothernHillsSoftware's Pocket Genealogist. Before moving to an iPhone, I had a SuperPhone (PDA and phone) and ran PocketGenealogist. It was a highly useful program and synchronized with my Legacy files directly. The Advanced version is $35 and well worth the price. It will sync with almost any computer based genealogy program.