I'd like to introduce a tool I've written, that I hope will make it easier to share objective-C code across iPhone projects.
The tool is Kit. To install it, you'll need the latest haskell platform release for OS X. Kit installs through haskell's package manager:
$ brew install haskell-platform # If you've got brew, otherwise: http://hackage.haskell.org/platform/mac.html
$ cabal update
$ cabal install kit