If you've had an iPhone or iPad with cellular networking for any length of time you've probably been notified about a carrier update. Some are mandatory and don't give you an option to say refuse or to be reminded later. Others just bug you occasionally until you actually perform the update. But why? What are they, what do they contain, and what do they want from us?
Carrier updates are used to help your iPhone and iPad communicate with the carrier network. These files typically contain information concerning voice networks, cellular data, voicemail settings, personal hotspot, and any other service your carrier provides. For example, with the recent AT&T visual voicemail issues on iOS 7, the only way for it to be fixed is through a carrier update, since it's part that makes iOS and your chosen network play nicely together.
This is why people that frequently switch between carriers by swapping SIM cards may receive carrier updates more often than people who keep their SIM card in just one iPhone. For example, if you travel and your iPhone 5s is unlocked, you can simply replace your AT&T SIM with a 3 UK SIM or any other international sim card you'd like. More often than not, the international carrier will push an update to your iPhone so it talks to the network better.
You can also check manually if you like by going to Settings > General > and About. When you swap SIMs you can almost always trigger a carrier update to appear this way. It's something I highly recommend doing when switching between carriers, especially when it's a carrier in a foreign country. The About section of your iPhone should also show your current carrier information as well, should you ever have to reference it.
If you ever experience issues with your network or you aren't getting the level of service as you think you should, it may be a good idea to repeat the steps above and see if a carrier update is available. Keep in mind though that carrier updates are only available for networks that Apple officially supports. If a specific carrier doesn't support the iPhone or cellular capable iPad in question, a carrier update would not be available. In that case, information such as MMS (picture messaging) settings and voicemail settings would need to be entered manually. This is a perfect example of the data a carrier update takes care of for you.
Next time you have an issue with your wireless service and the support rep asks you to read off your carrier settings information, you'll now know why they ask for that. Sometimes, being sure you're on the most recent version can solve lots of common problems such as picture messaging failures and visual voicemail issues.
What has your experience been with carrier updates? Have they remedied issues or just made them worse? If you have any other questions about carrier updates, be sure to leave those in the comments too and I'll try and answer them!