Who puts out the updates, and how are they delivered?
The updates can include changes from Apple or any of its official carrier partners, like AT&T or Verizon, or it can be a combination of both. (A couple of the wireless carriers I asked basically said, "It's an Apple thing — ask them.")
When one is available, you may receive a push notification on your iPhone or iPad, which you can download and install wirelessly. You may also get a message in iTunes the next time you connect your device to your computer via USB.
If you notice any network issues or problems using such features as voicemail, it's a good idea to check that you haven't missed a carrier settings update using the steps outlined above before contacting your provider.
Is there any way to see what the update is changing or fixing?
It's reasonable — smart, even — to want to know what's included in an update before downloading it to your iPhone or iPad.
Unfortunately, the companies don't make it easy to find out, if at all. It's not like a third-party app update, which often offers a change log to show you what's been added or fixed. In some cases, a provider might share details directly to the customer. Other times, the carrier might provide information on its website, though this usually involves digging through a myriad of support pages.
If all else fails, a Google search might lead to more specifics from an Apple or carrier-related user forum or site. But really, it would be nice if the parties involved spelled out the changes from the get-go, regardless of how big or small the update might be.
Are the updates safe to download? Is there any potential that the update might do more harm than good?
In general, the answer is, yes, they are safe to download. Apple's iOS mobile operating system is less prone (though not immune) to malware and viruses, compared with other platforms, like Android. Still, it's always good to keep an eye out for anything that seems fishy, like misspellings in the update message.
There is certainly the potential that an update might end up breaking something or negatively affecting your device's performance. We've seen this happen a few times with iOS updates. But this hasn't been a huge issue with carrier settings updates. If there is a problem, Apple and the carriers would assuredly issue a fix.