Steps to add an existing framework in Xcode 4:
1. Click the project in the project navigator.
2. In the project editor, click a target.
3. Select 'Build Phases' tab
4. Expand 'Link Binary With Libraries'
5. Click '+' button to add a framework.
6. Go back to the project navigator, you will see the new framework. You can drag it to 'Frameworks' group.