What do you usually do upon receiving an unknown call or missedcall?

It depends on the mood I'm in. If it is a repeat call then I might ask who they are and what they want. I have gotten repeat calls where the person keeps hanging up and then calls again the next day and then again. That makes me annoyed so that I will check it out. A missed call I won't purposely call back. There's too many missed calls. I am only interested in the ones that repeat and seem strange.

I ignore unknown calls or missed calls but what happens usually, I get a text message first telling who they are and they want to call me so I answer them. I have also answered unknown calls like calls coming from US because their number doesn't register on my phone so I ask them who they are and what they want.

I am different from you , usually when there are missed calls or unknow call,i will pass them ,and i will never call back them ,but maybe i will give them i short message to ask them if they have anything !but never a call , i think if they really get something with me they will call me again, if there are the same number called me several times i will call them back!