Here is when Android 4.4 is coming to your Asus PadFone3
Those with the Asus PadFone 2, Asus PadFone Infinity (in Russia and Asia) and the Asus PadFone A80 in Europe will receive the update during the second quarter of 2014. All other new Asus PadFone Infinity models will receive the update in the third quarter.
The Asus PadFone is a handset that powers a tablet when it slides into the dock at the back of the slate.
source: Asus via AndroidGuys