According to the report, "So what is in the update? After extracting the .ipcc file, we saw two new images. Both for AT&T's upcoming 3G MicroCell we wrote about here. The images will most likely be used to indicate if you are on the 3G MicroCell "Network.""
These images appear to be the ones that would be used to let you know if you are connected to a 3G MicroCell or not. They would more than likely appear next to the signal strength indicator that normally reads "AT&T 3G" in the US.
Carrier updates are described in this Apple Knowledge Base http://support.apple.com/kb/HT1970. Basically they are:
iTunes 7.7 and later has the ability to update the carrier specific settings on iPhone with iPhone 2.0 software or later. Carrier settings updates are small files (about 10k) that are downloaded from iTunes to be installed on your iPhone. The carrier settings can include updates to the default APN (how iPhone accesses the carrier's cellular data network), special dialing codes at Settings > Phone > [Carrier] Services, default settings for Stocks, Maps, Weather, and other items.
We covered the 3G MicroCellpreviously. We are not exactly sure who will be willing to pay a monthly fee to improve AT&T's service. However if you've been waiting to fix the problem yourself it looks like you won't have to wait much longer.