Sometimes I can't get incoming calls with my iphone 5c?

I live in a dorm and I guess it's logical that the walls/steel are blocking the signal or I'm interfering with other signals of different carriers. I have sprint. I have full bars and yet most of the time, I don't receive any of my incoming calls. My friends have said that it goes to voicemail after... show more I live in a dorm and I guess it's logical that the walls/steel are blocking the signal or I'm interfering with other signals of different carriers. I have sprint. I have full bars and yet most of the time, I don't receive any of my incoming calls. My friends have said that it goes to voicemail after a few rings.

I went to the apple store already, and the guy tested my phone. It worked perfectly fine (I'm a bit biased about the place.. as if everything will work in there). So I took my phone back and it still has problems. Sometimes it takes a while for the phone to make the dial sound when I'm calling others.

I have only dropped my iphone 5c probably three times, but I have a strong protective case that covers all over it. So far, no damages (knock on wood).

What's the problem here? Should I just keep taking it back to the apple store? It has a one year warrenty, but I can't seem to prove that somethings wrong it right then and there.
Update: When I mean by dropped, it's not a DRASTIC drop. It might have fell no more than 2 feet. My phone case has protected it.
2 answers 2