I had a blackberry storm 1 with asurion coverage. The phone bricked itself. I went into the store (had all the paperwork and reciepts etc, but nothing was needed) The guy pulled up my account, took my phone (nothing could be pulled off of it) and swapped it out for a brand new one. I didnt have to pay a single cent on it!
Just my experience,
Just go into your nearest store, and tell them that whenever you are trying to make a call, your phone screen will shut off and become non responsive MOST OF THE TIME. They will hopefully replace your phone for no charge. I would suggest you purchase the asurion coverage though. well worth the money for what it covers.