iPhone started dropping calls last night until I reset... is this common?

Recap: bought 8GB iPhone 3G on July 28th, and it has worked flawlessly since then. The phone itself never dropped calls, was getting great 3G reception here in Edmonton (on Rogers) and I was loving the phone.

Last night, my dad tried calling me, I would answer and then two seconds later the call would fail. I tried calling him, same thing. I tried calling other cell phones, other land lines, having them call me, etc-- I would sometimes not even be able to get through, the call would fail then, or it would fail after they picked up. Today I couldn't make any calls, period.

Today I did a hard reset - pressed and held the Home and Sleep buttons for 10 seconds - and now my phone works again. No dropped calls, great reception.

Should I be worried? Is this normal? What happened to my phone?

I don't want to take it in to Apple

 

Because I did a hard reset today and my problem seems to be solved. I had three people call me (two from cell phones, one from a land line) and called four different people, talked for 15 minutes on one of those calls. So maybe all it needed was a reset... but that leads me to ask this: WHAT happened after a month of running flawlessly and why did a reset help?

I'm going to monitor it for a few days and if it drops calls again I'll take it in to Apple. UGH.