Various reports are that fairly proficient C programmers starting with no iOS or Mac background have gotten non-trivial iPhone apps developed in from 2 weeks to 2 months. If you are not already a good programmer, then add between 2 months and 2 years, assuming you don't give up.
There are a few template generators that will allow a non-programmer to drop stuff into making an iPhone app, but they are extremely limited IMHO.