In general, you cannot call back a restricted phone number; however anecdotal sources suggest that you can dial *69 to call back the last number that called your phone but this will not remove restrictions. This way you cannot know the number.
You can also use a service to do the job for you, like TrapCall, it unmasks the Caller ID of blocked and restricted numbers, blacklists harassing callers, and can even record your incoming calls. There is no software to install, and it works on any mobile phone.
Ever get the feeling you're being watched? Check out some ways to keep your calls, texts, web browsing, and files away from prying eyes at PCmag.com.