does sim swapping (for vacations etc) disable LTE?

Discussion in 'Apple Watch' started by nicho, Mar 16, 2018.

  1. nicho macrumors 68020

    Feb 15, 2008
    if i put a different sim card into the iphone, does the LTE on the apple watch instantly stop working? Or will it continue to function as much as a watch where the phone is turned off/out of power would (IIRC there are issues with SMS messages and things?)
  2. Shirasaki macrumors G3


    May 16, 2015
    The watch will continue to work as usual, minus any internet connectivity as long as it is close to your iPhone. If your phone is away, LTE will work as usual.

    I haven’t tested overseas use. But your watch will simply pull everything from your iPhone as usual. My guess is watch LTE will not working if you leave your phone alone. But anything else should work as usual during your trip.
  3. nicho thread starter macrumors 68020

    Feb 15, 2008
    Ah yes, I don't expect the LTE to continue working abroad (because roaming isn't supported, and as I'll be buying the China model it's impossible to make it work elsewhere).

    Main thing is I want a way of making emergency calls and/or sending messages while a different sim card is in the paired iphone. I wonder would i have to activate airplane mode on the iphone or does apple watch default to its own LTE connection if the iphone has no service?
  4. Shirasaki macrumors G3


    May 16, 2015
    Apple Watch won’t go to its LTE service even if iPhone has no service. Apple Watch only goes to LTE when iPhone is disconnected from watch.
    I wonder why you want to buy China model? LTE watch is not even available in China anyway.
  5. nicho thread starter macrumors 68020

    Feb 15, 2008
    Because I live in China?

    The LTE watch been available from day 1 in China, although the service not so much... China Unicom have launched support for it though and it'll be coming to my network soon.
  6. nnoble macrumors 6502

    Jun 19, 2011
    Nicho, when is the service likely to begin and how much will it cost? I too am in China and would be useful to know if you have the answers.
  7. dave006 Contributor


    Jul 3, 2008
    Just West of East
    No, swapping in another carrier's nano-SIM in your paired iPhone does not disable your watch's ability to use LTE as long as you are still in your carrier's network. The LTE watch can't roam. It is assigned a unique phone number from your carrier, this is what allows your watch to make native LTE calls that appear to be from your iPhone's phone number.

    However, as your call is passed through your carrier's network, the phone number of your paired iPhone is assigned. Anyone that receives a call from your watch will only see your iPhone's phone number. This is why roaming is not supported since the phone number magic is done within your carrier using a specific configuration process.
    No, LTE on your watch will still work the same as long as you are within your home carrier's network. Once you leave your home carrier's coverage area your watch can't use LTE since roaming is not supported as explained above.
    Yes, your watch will behave as if your iPhone were powered off when your watch is out of Bluetooth or Wi-Fi range of your paired iPhone. Note: to receive SMS / MMS Txt messages on your watch when you are not in BT or Wi-Fi range of your iPhone, your iPhone must be on and connected to your carrier's network via a cellular connection or via the Wi-Fi Calling feature and your watch must have an active LTE connection. This is to allow your iPhone to receive the SMS / MMS Txts and forward it to your watch via a BT, Wi-Fi or LTE connection.

    As long as your iPhone is powered on, even with a different nano-SIM and your watch is in range (BT / Wi-Fi), basic functions will continue to work since the watch depends on the iPhone for connectivity by default to conserve battery. LTE is only used as a last resort or when your force your watch to use LTE, by turning off BT and Wi-Fi.
    Again, your watch can only use LTE when within your home carrier's coverage area due to the "No Roaming" restriction on your watch's LTE service. You don't have to activate Airplane mode on your iPhone but you would need to turn off Bluetooth on your iPhone. Your watch can manage both Wi-Fi and LTE but Bluetooth is managed on your iPhone.

    So if you are on vacation in another country, you can use your watch and make Wi-Fi calls when your iPhone is not near by if you are connecting to a "Known" Wi-Fi connection that your iPhone had already connected. When traveling, your watch will not be able to make or receive direct LTE cellular calls!

    Note: once you pair your iPhone and watch and activate your watch's LTE with your carrier, then you can determine when or how to use LTE on your watch even if your switch the nano-SIM in your paired iPhone. However, your watch will not be able to use LTE unless you are still within your home carrier's service area.

  8. nicho thread starter macrumors 68020

    Feb 15, 2008
    Thanks for your answer @dave006 - so it basically works as I hoped it would.

    if the nano-sim matching the watch LTE is put into a different iphone (and left at home) would this also work?
    --- Post Merged, Mar 17, 2018 ---
    I'm only looking for it to work in my home country anyway - the SIM in the phone would work for the other country.
  9. Shirasaki macrumors G3


    May 16, 2015
    Oh. That makes sense then. Are you going to use the LTE watch in China? I am just curious. What network are you using right now?
  10. nnoble macrumors 6502

    Jun 19, 2011
    The answer will be different, one Chinese Province from another. For example, China Unicom will do one thing in one province while introducing something different or later in another. Unicom did offer an Apple Watch LTE service originally in some areas, but then it was withdrawn for security reasons. Probably inability to track; I don't know for sure. It will be re-introduced once these issues have been resolved. I'm interested in the pricing of such a service, as and when they appear. Meanwhile, my Fitbit is dying having just barely survived a very long wash cycle. The future might be AW for me, although I really do like Fitbit's simplicity and long battery life.
  11. nicho thread starter macrumors 68020

    Feb 15, 2008
    It is resolved... but only launched in Shanghai, Guangzhou, Changsha, Shenzhen, Tianjin, Zhengzhou. I'm in one of those, so I'm expecting similar cities to work for China Mobile (my network).

    As to cost... all I can find from Unicom without being their customer is "the first 12 months at a lower cost" but no indication of what that cost will be. China Mobile is quite expensive compared to Unicom so I might end up being put off but... right now I'm leaning more towards going for it than away.

    Until that time I'm sticking with a series 0 and series 2 in rotation. Worst case I might end up waiting til September or October for a series 4, which financially might not be the worst thing.

Share This Page

10 March 16, 2018