You've always been able to make a voice call by speaking into your Apple Watch, or share your jogging route over the internet in real-time - but only if you lug an iPhone along, too.
Paging Dick Tracy: Spark's eSIM launch means we finally get a cellular Apple Watch
To take advantage of this functionality, you need an Apple Watch Series 5 (GPS + Cellular), priced from $929, plus Spark's new $12.99 per month One Number Wearable Plan.
Available from December 6, the Wearable Plan lets your watch share your smartphone's calling and txt plan, whatever that is (again, without the need to tethered), and it also throws in unlimited data specific to your wearable (in this case, your Apple Watch). Technically, it's not unlimited because there's no hot-spotting and you'll be throttled after 40 gigabytes - but given the lightweight nature of Watch apps, it's hard to see anyone getting anywhere close to that limit.
The One Number Wearable Plan is currently only available for the Apple Watch Series 5, but Spark says it'll be expanded to support other devices in future.
Earlier, Telecommunications Users Association head Craig Young told the Herald that phone companies had been reluctant to offer eSIMS - because offering you a mobile number via a SIM card-free process would make it easier to switch between carriers.
But now that Spark has crossed the Rubicon, its rivals are sure to follow - although the timetable is hazy at this point.
"We remain committed to delivering eSIM support on our network in the future however the roll-out in New Zealand has been delayed due to a range of factors. Our team is working on a release as soon as possible, but we are unable to confirm a date just yet," a Vodafone NZ spokeswoman said.
A spokeswoman for 2degrees said, "We are looking at how we might bring this technology to our customers. At this stage, we can't say when that will be."
Spark offered is first eSIM support back in April, when it introduced support for the technology in Apple's latest iPhones (eSIM support has been a mainstay for high-end models with all the top handset brands for a while now - it's just been, as with smartwatches, that there's been no mobile carrier in NZ to support the capability).
Whereas an eSIM setup can allow an iPhone and an Apple Watch to share one number, it can enable one handset to host two phone numbers - a boon if you want to juggle home and work numbers on a single handset, or if you're travelling and want to buy a local phone account without the need to faff around swapping out a physical SIM card.