Yes, it is possible to build frameworks so the user of the framework can't see the source code.
Check out these articles (I've successfully used the first one to create frameworks in the past -- the later articles are updates to the original):
http://www.drobnik.com/touch/2010/04/making-your-own-iphone-frameworks/
http://www.drobnik.com/touch/2010/05/making-your-own-iphone-frameworks-in-xcode/
http://www.drobnik.com/touch/2010/10/embedding-binary-resources/
To use the framework, your users would just drag the .framework bundle into Xcode. They will be able to see the header files you copy into the bundle (see the articles above), but not the source (as it's not included -- only the compiled output is in the bundle).
This can also be a great way to distribute code that is used for multiple projects within your company.
Update:
Check out the link featherless added below -- it is much more recent and all on one page: http://github.com/jverkoey/iOS-Framework. It also lays out the issues with several other approaches. This is the guide I now follow when trying to remember what to do when setting up a new framework. :)
Update2 (with Xcode 6 release)
There is a option, exactly that you a re looking for:
Universal Framework for iOS!
Will be my code visible to others? A: No. This Framework will export a compiled binary, so anyone can see inside it. You can make the same for some other files, like XIBs.
Why I need this? A: This is for developers/teams that want to share their codes without shows the entire code (.m/.c/.cpp files). Besides this is for who want to organize compiled code + resources (images, videos, sounds, XIBs, plist, etc) into one single place. And this is also for that teams that want to work together above the same base (framework).
(c) http://blog.db-in.com/universal-framework-for-ios/
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