Simultaneous Voice and Data enables CDMA2000 users to access the web, send emails, play games, view photos, watch videos and use data intensive GPS navigation option like updating maps or downloading traffic info while simultaneously communicating on a phone call.

Previously, if a subscriber accepted a voice call while using the data connection (e.g., while viewing a video), the data session would be suspended.

Most dual-antenna EV-DO devices will support SVDO through the use of a separate transmitter and receiver for the active 1X voice and EV-DO data traffic.

No changes to network infrastructure is necessary to implement SVDO. 

More on Simultaneous Voice and Data (SVDO)

The Perceived Value of Simultaneous Voice and Data (SVDO) Transmissions
By CDG, July 6, 2011