According to Apple, the latest version of iOS made a change to a government-regulated feature (a requirement of the 911 act) that requires all smartphones in the United States to be able to dial 911, even if the phone doesn’t have network access. This means you can access emergency services on any iPhone (and Android), even if you don’t pay for service from the company that the phone is tied to. For subscribers, it also works if you happen to venture away from cellular coverage.
It makes sense, then, that the “SOS only” label replaces the carrier’s name in this instance. Most people only started noticing this change as of the iPhone 14’s launch, but it should apply to any iPhone on the latest version. You may not see it if you don’t live in the United States, Canada, or Australia, however, as the emergency dialing feature is only available in those three countries as of writing.
If you ever notice this on your iPhone and you’re certain you should be within range of an appropriate cellular tower, you may want to try toggling cellular data off and then back on (found in Settings > Cellular). If you’re in international territory, make sure you’ve turned roaming on. When all else fails, powering your iPhone off and on can also fix the issue. Otherwise, you may need to give your carrier a call to see why its network is rejecting your iPhone.