iPhone OS for Cocoa Developers

If you are an existing Cocoa developer, many of the frameworks available in
iPhone OS should seem familiar to you. The basic technology stack in iPhone OS
is identical in many respects to the one found in Mac OS X. Despite the
similarities, however, the frameworks in iPhone OS are not exactly the same as
their Mac OS X counterparts.

If you plan on migrating an existing Cocoa application to the iPhone OS
platform, you need to consider the differences between the Mac OS X and iPhone
OS platforms and adjust your plans accordingly. You can find an overview of the
platform differences, along with a discussion of migration techniques, in Migrating from Cocoa in iPhone OS Technology Overview.