My First Hard Freeze...

Today I experienced my first hard freeze on my iPhone. I went to the doctor for a routine checkup. While I was waiting, I went to Appleopolis and checked it out. Pretty sweet. I turned the phone off when the doc came in (actually, just hit the sleep button), and on my way out I was making my appointment for my next visit - so I took the iPhone out. He says, "ooooo, is that the new iPhone?". And I say "why, yes it is!" and I proceed to swipe the unlock, hit the calendar button, and

WHAM!

Locked, hard. Completely non-responsive. Needless to say, a bit embarassing.

So I press the home button for ever, and it wont kill the Calendar app. I hold down the sleep and home buttons, and the phone shuts down after 10 seconds. I hit the sleep button again, and it turns on with the while Apple logo. Phone boots, and I am back in business.

The only "weird" thing I was doing was browsing apps at Appleopolis with Safari. I was using the Gas App (to see where cheap gas prices are), the Movie App, and some other couple of Apps I cant remember. I was adding some icons to the Appleopolis dashboard when I turned the phone off.

Any ideas what could have caused the freeze?