Is there a way to block callers for some reason?

Like if i block him, he'll get a busy tone, phone switched off, or something else.
Need to know how to do that on iphone.

To so anything other than just keep the phone from ringing on your end, and the call goes to voice mail, you will need to download a call blocking app, that has features you want when the blocked caller calls, things like pickup and hang up, voiding going to voicemail. Messages to fake them into not calling any more thinking your number has changed or something.