Before this update, if you are in a non-EVDO area and your phone is using a data connection (activesync with exchange server, internet explorer, etc.) an incoming call would go straight to voicemail. In an EVDO (high speed) area, an incoming voice call would temporarily stop the data connection and the phone rings.

Once this update goes into effect, incoming calls will break through the data connection in non-EVDO areas. If you use data on your phone and don't live in an EVDO area, this will be a nice improvement.

Hope I clarified things for you.