Although cellular versions of the Apple Watch Series 3 nominally need to be linked to an iPhone number to make calls, they may be able to dial emergency services even if their phone/data service isn't activated.
After a first unsuccessful attempt to test the "Emergency SOS" feature on an unactivated Watch running watchOS 4.1, a Reddit poster said they recently emailed Apple asking if it was a carrier issue and if support was ever planned. The person then received a reply from Apple Executive Relations, eventually getting a mediated explanation from engineers that a Watch should be capable of making SOS calls with or without activation.
On a second test after installing watchOS 4.2 beta 3, the poster managed to get in contact with 911 after waiting 3 minutes -- having been encouraged by an Apple representative to wait up to 5. It's not clear if the OS update had any impact.
Emergency SOS is triggered by holding down the side button on a Watch, which will eventually dial the emergency dispatch in a given region. Once that call ends, a Watch will attempt to fire off text messages to listed emergency contacts, including location information, even if Location Services are normally turned off.
AppleInsider has yet to independently verify the Reddit claim.
If true, though, it could make the cellular Series 3 appealing to people who would otherwise pick a GPS-only Watch. While the GPS Series 3 starts at $329, cellular models are at least $399 before any monthly data fees.