We already know that one does not simply walk into Mordor -- even though a pair of nasty hobbitses pulled it off just fine -- but a trip to the mountain of fire would have been a lot easier for the Fellowship if they had an iPhone handy.
For a crew of heroes as fond of the drink as the Fellowship is, an inn/pub/shop finder like AroundMe would have made their trip a lot more enjoyable. Sure, Frodo and his hobbit buddies had opportunities to relax a bit in Bree (before the party was crashed) and took a bit of a breather in Rivendell, but once they departed toward Mordor, it was all business. Call me crazy, but I think a few more detours to tucked-away pubs (or maybe even a smoke shop to stock up on some Longbottom Leaf) would have been well deserved.
After leaving Hobbiton, it became immediately clear that Frodo and his companions were woefully unprepared for the varying climates the trip would have to offer. If they had access to the Yahoo Weather app -- which lets you check the current conditions and forecast for multiple locations at the same time -- they might have packed a few more layers for the journey.
Lembas bread might be fine for the average man, but the hobbits have appetites that would make a troll blush. BigOven features more than 250,000 recipes, and can be filtered by whatever ingredients you have on hand. Samwise knows his stuff when it comes to wild edibles, and with a tool like BigOven he could have whipped up a nightly feast using whatever was available on the trail.
This one is a gimme. Google Maps is the go-to navigation app for iPhone users, and that's because it's everything that Apple Maps isn't. It's accurate, it's pretty (enough) and it won't tell you to drive off of a highway overpass. When it comes to a trip from the Shire to Mordor, Google Maps could have helped Frodo avoid several hazards, including the almost-lethal trip to Minas Morgul, which results in a paralyzed hobbit and an almost-lost ring.
Despite the fact that almost every creature we see in Peter Jackson's LOTR movie trilogy speaks pretty good English -- including the orcs and Sauron himself - Middle Earth is filled with strange languages. With instant translation from iTranslate Voice, Frodo could have used diplomacy to bring Sauron's reign of terror to an end. You never know; after speaking with the dark lord in his own tongue we may have found out that the whole thing was just a big, terrible, apocalyptic misunderstanding.