Many transportation options in this region have been negatively impacted by the insurgency. I know that rail service has been discontinued after insurgents used explosives to derail a train.

I think Phuket Airlines might still offer service between HDY and HKT. Other than that it would be car, bus or mini-van (~ 450 Km). You could inquire in the Phuket or Southern Thailand sub-forums on ThaiVisa.