2

If a user goes outside with the Apple Watch Series 3 and keeps their iPhone at home, how will the calling feature work?

2

The Apple Watch Series 3 GPS + Cellular has LTE built-in. Here are the bands supported by the USA version:

LTE
2 (1900 MHz)
4 (AWS)
5 (850 MHz)
12 (700 MHz)
13 (700c MHz)
17 (700b MHz)
18 (800 MHz)
19 (800 MHz)
25 (1900 MHz)
26 (800 MHz)
41 (TD 2500)

UMTS
800 MHz
850 MHz
1700 MHz
1900 MHz

SOURCE

That same page also lists the bands for other countries.

2

The most relevant part to making the Apple Watch 3 (with Cellular) work without having your iPhone nearby is the eSIM (electronic SIM* or Subscriber Identity Module).

Obviously, having LTE capability is important, but what sets it apart is the eSIM's ability to share your existing wireless account info including the phone number and data plan.

One of the most interesting aspects of the Watch 3’s eSIM is that it’ll share your iPhone’s number. You can think of them as part of the same connection. However, this also means it’ll only work with an iPhone – and that your iPhone and Apple Watch will have to be with the same network provider.

From: What is an eSIM? The Apple Watch Series 3’s new SIM tech explained

When you have this capability, the Apple Watch appears to the carrier as just another device and when a call comes it, will route it to both the iPhone and Watch.

You also have this ability with respect to data, incoming and outgoing traffic gets authenticated to the network as any other device would which is how you can stream music while you run without carrying your phone.

There is a limitation however. Your device and your carrier must support this technology. You also cannot have a data plan on carrier A and voice/text on carrier B.


* A subscriber identity module or subscriber identification module (SIM) is an integrated circuit that is intended to securely store the international mobile subscriber identity (IMSI) number and its related key, which are used to identify and authenticate subscribers on mobile telephony devices (such as mobile phones and computers). It is also possible to store contact information on many SIM cards. Source: Wikipedia

  • Nice answer +1. Hope you made it through Irma okay! – user3439894 Sep 13 '17 at 18:39
  • I did, thank you. But many roads are impassible and gas is next to impossible to find, so still hunkering down. It amazing how one storm can send you back to the stone age. – Allan Sep 13 '17 at 18:41
  • eSIM has nothing to do with sharing a phone number, it only allows to load SIM data like auth keys remotely without actually putting in a physical SIM, however as far as the phone number sharing aspect is concerned there is no difference between eSIM and a real SIM - both appear as separate devices to the mobile network. The number sharing part is handled by software in the mobile network which knows when a call comes in it should route it to both SIMs, and similarly when an outgoing call is placed from the watch it knows that it should set the caller ID to your main number. – André Borie Sep 24 '17 at 0:53
  • @AndréBorie - if you can get a SIM (micro or otherwise) into a form factor that fits on your wrist then your argument would have merit. The whole point of my answer is the fact that the watch makes use of eSIM which now enables it to have cellular capability. – Allan Sep 24 '17 at 0:58
  • Sorry but you said yourself that "what sets it apart is the eSIM's ability to share your existing wireless account info including the phone number and data plan" - that is not the case. eSIM is just a new "form factor" for a totally normal SIM, the number sharing logic is added down the line in the network. In fact the SIM (physical or eSIM) doesn't even know nor care about its number. – André Borie Sep 24 '17 at 12:23
-2

The user receives the call on their watch since it has LTE hardware built in.

Some of the information contained in this post requires additional references. Please edit to add citations to reliable sources that support the assertions made here. Unsourced material may be disputed or deleted.

  • Do you have a source? – JMY1000 Sep 13 '17 at 4:45
  • Your statement is only true if one has the Series 3 GPS + Cellular Apple Watch, it is not true for the Series 3 GPS Apple Watch. I'd suggest you improve your answer with references from Apple's web site on this product, so as to avoid down-votes for statements that can be both true and false at the same time as written. – user3439894 Sep 13 '17 at 17:58
  • ¯_(ツ)_/¯ If someone asked how cellular worked on an iPad would anyone assume were talking about a wifi iPad? – Steve Moser Sep 13 '17 at 20:01

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