Previously, I mentioned Characters here on TUAW as one of my favorite iPhone apps, and here's another good iPhone app that will assist you with playing a great MMO. EVE Tracker is available in the App Store right now for free, and will let you track your EVE Online skill training (which can happen even while you're away from the game) from anywhere an iPhone can get online.
Just punch in your API account key, and just like EVEMon (a great EVE character tracker which isn't yet available for Mac -- hint hint EVEMon devs), you'll be able to see what your character is learning, where you're at in the skill trees, and so on. Also like EVEMon, you can't actually play the game from the app, but if you're away from the client and need to know just when that cruiser training will be done, it'll do ya.
It's too bad we haven't seen more official clients for the iPhone -- Blizzard and CCP both have been rumored to be working on mobile clients for at least parts of their games, but the App Store has only seen unofficial software for now. Someday, we hope MMO players will be able to play the AH or check their in-game mail from the iPhone, but for now, stuff like EVE Tracker is what we've got.