Found a solution for the missing Mobile Data button, at least on Verizon Galaxy S3. Instead of the Gear icon, choose the one next to it (three squares and a double arrow - don't know what it is called!). That lists the possible items for the Notification bar at the top. You can click and hold any one of the items shown, and then drag it where you want it. Just do that with "Mobile Data", and drag it up to the first line, and then it should appear. You can also pick other things to appear, and change the order, if you want.