Zong's voice calling is bad in Islamabad. I Ported to it Two years ago on Volverine's insistence but Others couldn't Hear me so i Tossed to Mobilink.
Then, Last year when Zong brought about 4G, my elder brother converted to it and had the Same complaint.
On the Other Hand, Volvi himself was satisfied in Abbottabad/Manshera region.
But yes, since this topic is on 3G/4G, Zong's 4G gives bro 24-28 mbps.