Why does my iphone 5 say unknown when receiving a call?

When I receive a phone call, my phone's caller i.d says unknown. It doesn't matter if I have the caller in my contact list. Does anybody by any chance know how to fix this? I have an iPhone 5 on the sprint carrier. Thank you

Added (1). It's not that, I've called myself from another phone to see what would happen. No luck

Added (2). I dialed my phone number and called myself from my girlfriend's phone. Thanks anyways guys. If anything comes up I'd appreciate any help

The person calling you probably has their number blocked on their end so it's showing up as unknown on your phone.

It's a blocked #

Well if it says unknown the caller called you private, either for safety or for others don't want you to call back when they call from a phone or other types of reasons why. Unknown usually appears as private or as just the number with no name or city and state. If the caller told you it didn't call private, then something is wrong there. Then you should take it to the sprint store or call custer service on sprint or email sprint to see who can help you fix it. Have a great day.

Try this go to settings and scroll down and find phone click that and find show my caller id click that and turn on hope this helps.

This happened to me once. I have an iPhone 5 and sprint too. And then when I pick up it showed the persons name. Never happened again. Glad I'm not going crazy though.