Apple does not have a first-party presence in Pakistan, however the company does sell its iPhones and iPads through third-party authorised resellers and cellular carriers. The iOS devices sold in Pakistan through these official channels are same as the rest of the world, except these devices have FaceTime video and audio calling disabled by default. This is not different than the iPhones sold in many middle eastern countries, that also don’t allow the use of FaceTime feature.
With iOS 12.4, Apple has lifted the restrictions on FaceTime feature for iPhones and iPads sold in Pakistan. This essentially means that if someone has purchased an iOS device through Apple’s official resellers or cellular carrier, they can simply update their device to iOS 12.4 and enable video and audio calling through FaceTime.
This brings the devices sold at official Apple resellers in-line with devices being sold in Pakistan’s grey markets, which are usually imported from the US and European countries and offer FaceTime functionality like the rest of the world.
To update your iPhone to iOS 12.4 simply launch Settings -> General -> Software Update. Or download the iOS 12.4 direct IPSW files here to install the update manually through iTunes.