No, there is not all the hardware.
The 3G modem/radio in the Kindles are "data channel only" devices, no voice channel support.
Ref:
http://m2msupport.net/m2msupport/any...dpa-3g-module/
On the other hand, search and you will find a demonstration of VoIP for the Kindle's.
One of the last things twobob did before he left.
I am pretty sure it was for a K5 (KT) and I don't know if a DX has the horsepower for that application.