Why will my droid incredible not receive phone calls at times? Just goes strait to voice mail.

It is quite possible that it does not have a signal at the time. Check your call coverage. Keep in mind that at the top it will usually display your 3G coverage. Get the app "Real Signal". It should allow you to display your CDMA coverage in the status bar at the top. Otherwise make a call and you'll notice that your bars change from 3G to CDMA.

I don't live in a 3 g area but most of the time I have 3 to 4 bars of signal

First try disabling any 3rd party apps to ensure this is not the problem. Then I would try backing up anything important and restoring the phone.