This will only work if you're connected to a 4G network or WiFi. There is no app that will enable this on a 3G network.
The issue isn't hardware or software related, but rather the CDMA network that Sprint uses. It is limited to only voice or data at any given time. That being said, the reply regarding 4G is correct in stating that if you're connected to 4G you will be able to to be on a call and use data at the same time. The other way to achieve this is to be connected to a wifi network. If you're on wifi you will also be able to use the phone and use data at the same time.
You can do it with the new HTC EVO 4G LTE.