I do not own an iPhone, though i do know people who do. The telephone I own is a Samsung Omnia. It's a windows mobile powered phone for Verizon, which is plenty powerful. I like it more than the iPhone, which is why I have it. We have a lot of applications for our Windows Mobile phones which mirror the iPhone's apps, and a bunch of them are tuner programs. I've tried them all, seriously. None of them are truely up to spec in my opinion. Case in point:
If you tune it with x tuner program, then jack directly into a real tuner (mine is a Korg CA-30), the tuner will tell you the tuning is off. Personally I trust the tuner over the phone tuner. I'd recommend doing the exact same thing I did. The iPhone does have a lot more developers for apps, therefore you might have a good tuner out for your phone. Unless you test it like I did with our Windows Mobile ones, you won't ever really know. In the end, IMO and IME, it's just cheaper to get a real chromatic tuner like the one I use. You may get lucky though and the first app you try just works.
Furthermore and somewhat off topic. Computer programs are great, phones now are nothing more than computers. I use programs on my PC's at home/work/on my phone all the time and the ones I use 99.99% of the time I have complete assurance in. Something like a tuner I do not. It's too important a tool to trust to something not designed specifically for the job. If you do try this, please please test it with a real tuner. Make sure the results you get are accurate, then post so other people know. Don't just blindly assume that a program does what it's supposed to because they say it does. I'm sure you won't, as you're asking here. You guys with the programs try that out and tell your results as well.
There is a lot to be learned from this thread! Thanks for posting it.
Scott