Aaqib Hayyat :
well it depends on case by case basis ,
sometimes we receive interview call letters , sometimes sms/calls on mobile numbers. Interview are mostly taken by the client of NTS , I have not seen any lit of interview etc on nts site ,except a few ones like NAB DAD/ADs.

So expect a call/sms then letter , but also visit nts site as well, this is the rarest chance.
Mere saath ek case ma yeh hua tha k mijhe call letter interview dene k baad milla tha .So keep you cell no. active.