Yeah thats what the problem is with Zong, or else its the best amongst all other options.
WIth Charji, you need HUWAEI or ZTE device that allows you to portforward, then you are good to go. With out portforwarding you get NAT 3 and that restricts the party formation and Audio chat. For NAT2 you need the Huwaei deivce ( wingle also lets you port forward as its huwaei). In short dont get the GADGEiT device they are offering.
Charji is all about signal strength. With zong i get solid speeds of 20mb up and down with a extremely good pings. With Charji the connection is stable but the speeds are only 3 down nd 1mbps up. So yeah there is a hell of a difference. I have 8mb broadband PTCL and when its stable its just as sweet as zong but NAT2. If your land line is messed up than Zong 4g is the best.