If I need to present my iphone app idea to an investor, is it best to have a prototype of the app or just a formal design on pdf/psd? or are they the same? if not, what is the diff?
If it's the early stages of talking with an investor, wireframes (psd or otherwise) are probably the best way to go. Although it's nice to have something working, unless it's really good you might be tripped up by the deficiencies of a prototype or alpha version. There are some excellent resources for wireframes at Smashing Magazine http://goo.gl/nd0o
thank you!
You mean an Alpha or Beta version? Prototype's generally don't fall into the software specific region.