If you look at your device info under settings you should see a radio version of HA00_140. The update on the audiovox site updates this to HA01_140. I just got the 6600 as a replacement to my 6601. I wasnt going to do the upgrade, but last night my phone would not ring when I had incoming calls. The screen would not even show me an incoming call. I only knew I had missed calls when the phone beeped to alert me to a missed call. I checked all the settings and volume and everything was fine. I ended up having to do a hard reset. All in short, I think I'll try the upgrade. Afterall it updates the radio in the phone so it cant hurt.

My Arsenal:
PPC6600...'nuff said