I solved this problem by copying Phidget21.framework to /Developer/Library/Frameworks and referring to this in XCode.

After upgrading from XCode 4.3.x to 4.4.1, I'm unable to link my Phidgets-based application. The symptoms are: 1. When I try to add the Phidgets21 library/framework to the project, it doesn't appear in the provided list of frameworks, and has to added manually (from /Library/Frameworks/Phidget21.fra...