How to run a script after Xcode runs codesign on my iPhone app?

Can you create an aggregate target that contains both your "Ad hoc" target and a run script build phase (that runs after the "Ad hoc" target)?

A short update on that topic: Since we all use Xcode 4 these days. Apple has refined the process of running scripts on several events in the build process with the introduction of schemes.

Go to Product → Edit Scheme… and expand the Build side bar item, there you have the chance to run scripts before (Pre-actions) and after (Post-actions) a build, a debugging, archiving, etc event. It's pretty handy to set a version number from git describe output or upload .xcarchives to services like TestFlight and HockeyApp.

If you want to share your pre/post scripts with other team members who got access to your code repository, you can go to Product → Manage Schemes… and mark your scheme as shared. After you checked in …{project_name}.xcodeproj/xcshareddata/xcschemes/{project_name}.xcscheme to your preferred scm everybody can use it in the project.