bab2010 said:What is a carrier update? What is a firmware update or update?
A firmware update is what you get when you upgrade in iTunes.
Carrier settings updates are small files (about 10k) that are downloaded from iTunes to be installed on your iPhone or iPad Wi-Fi + 3G. The carrier settings can include updates to the default APN (how the device accesses the carrier's cellular data network). The carrier settings for iPhone also include special dialing codes at Settings > Phone > [Carrier] Services, default settings for Stocks, Maps, Weather, and other items.