How to find out who's calling me private?

Any apps? I don't wanna make it a big issue but every now and then i'm getting calls like this. Apps for an apple, iphone!

You can go back through your phone records and you will get the number there if they just hid the caller ID. If they called you from a voice- over IP line it is a little different. First you would have to go back through your phone records, get the number that called you, find out who the provider is (i.e. Skype), contact the provider, then get the IP address.