A very popular ap for the iphone is a digital ocarina by smule. It produces fabulous sounding music and only costs $1 for goodness sake. I must admit that I am tempted (time and again) to get an iphone but the $75/month for data/voice is way more than I want to pay these days. That's close to $1000/year for cellphone service. Bleah.

The ocarina is an ancient family of instrument (believed to date some 12,000 years), and one of the easiest instruments to learn. The Smule Ocarina both preserves this instrument and extends/transforms it for your iPhone. Blow into the phone/instrument. Control pitch with different fingerings. Learn to play countless melodies. Find out more about the history of the ocarina at Wikipedia.