If you start doing some reading, over at xda for instance (and other sources), you'll see that it's a big issue. Although Qi is the most popular standard, and LG intended the G3 to be Qi enabled, AT&T as usual did everything they can to make the phone as bad as possible for customers.
There are two standards; PMA and Qi. Everybody likes Qi and there are hundreds of options/accessories at good prices. PMA (Pwer Matters Alliance) is a different standard, and in fierce competition to Qi. AT&T has bought stock in PMA. Therefore, they will do everything they can to kill any customer use of the competition, Qi. Even though there are not many options for PMA charging, and even though AT&T itself can only sell one accessory; the Circle Case (for $60!). Then you go get a cheesy Duracel power mat for the actual charging. Duracel is a member of this PMA group as well obviously.
As if this were not bad enough, many AT&T G3 owners are experiencing problems even using AT&T's system!! Apparently if you get the circle case, it can stop functioning at any point. Reportedly AT&T has unofficially stated to one xda member that they know there is a problem with their G3 and wireless PMA charging can quit at any point. It's either software or some hardware goofing that AT&T did. Many users have replaced phones and circle cases many times and are still left hanging. So get out your voodoo dolls, stick an AT&T invoice inside the head, and start sticking pins in it, because that's about the only progress you will make with AT&T (may leeches infest their undershorts).
Some people report success cutting open the circle case, getting the sticker out of it, and pasting it into the back cover of the phone.
There' s also the more global issue that the phone is set up for Qi charging by LG out of the box in Korea, but all the US carriers do not sell the phone ready for charging. They make you buy something additional to get this functionality. Typical greed and lack of concern for customers. Except with AT&T, regardless of what you pay, you reportedly cannot get reliable charging- even PMA.
If I'm wrong with any of this, please correct me. If anyone has found a solution to get PMA charging working reliably, long-term, with an AT&T G3, please let us know.