Can I record audio from another app (Phone, FaceTime, Skype, …)?

Having multiple apps use the mic at the same time is not officially supported in iOS. It is currently not possible to record phone calls. The current version of Skype will not let you record calls (but older versions did, so Skype might change this again).

You might be able to record audio from other apps by following these steps:

Also make sure that both the sound of the app and the sound coming from the mic are being recorded.