Freezing, dropping calls...help!!

Ok so this was a minor problem when I got my new iphone 4 on sunday but now its doing it with every call. I was talking to my bf earlier and the phone just went black wouldn't let me turn it back on...then he called me back...it rang but when i went to answer it wouldn't let me slide the bar to answer. In fact touching the screen did nothing. This kept happening over and over. Anyone else having this problem?