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AT&T unveils NumberSync, a network-level feature for sharing your phone number with connected devices

Apple Continuity

Apple has been building Continuity features into its software that let you make phone calls and send messages from iPads, Macs, and Apple Watches through your iPhone for a while now, and today AT&T is announcing a new network-level advancement called NumberSync capable of doing that for all connected devices.

With NumberSync, AT&T customers will soon be able to use what’s called mobile twinning to share a single phone number with multiple SIM cards in smartphones, smartwatches, tablets, and other connected devices. The goal is to let you send and receive phone calls or messages from all your connected devices without relying on a specific app or operating system feature.

NumberSync won’t immediately benefit iPhone, iPad, Mac, and Apple Watch customers, but it is an advancement that prepares AT&T’s network for what many consider just a matter of time: Apple Watches with built-in cellular connections and possibly one day cars.

Even before Apple Watches become untethered from iPhones, AT&T’s NumberSync feature will soon be able to benefit other smartwatches that already ship with SIM cards but have their own phone numbers for making phone calls and handling messages.

NumberSync won’t require smartphones to be on a Wi-Fi network, connected via Bluetooth, or even powered on for other connected devices to work with your real phone number. This also unifies your voicemail inbox to one phone number if you miss or can’t take calls.

As for availability, AT&T says its focused on supporting NumberSync through an ecosystem of devices with the first supported device expected soon and more to follow before the end of the year.

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  1. Iven Tenz (@ivenalot) - 7 years ago

    T-Mobile does it better in my opinion via iCloud. its called iPhone Calls to iPad and Mac. Meaning: “Allow other devices signed into your iCloud account to make and receive calls using your carrier account even when your iPhone is not nearby”.

    • Eric Cirone - 7 years ago

      That’s Apple, not T-mobile and it’s described in the first sentence of this post.

      • Iven Tenz (@ivenalot) - 7 years ago

        It is T-Mobile, and its new. Do your research.

      • Terrence Newton - 7 years ago

        The new advanced version of Continuity, which is only supported by T-Mobile currently (though I’m not sure whether it’s publicly available or not) doesn’t go through your phone. Rather, it goes from your device (Mac, iPad, etc.) directly through the internet. Same thing for the text messages.

      • Howard DeMarzo - 7 years ago

        just to add to this comment, Didn’t t-mobile have a major breach, very recently…..btw thats a rhetorical question. T mobile isn’t getting any of my business. besides apple is already doing call and texts thru your other devices. and it works VERY well. so by all means give t-mobile your business when the feature is FREE on all apple devices already. more like t(asteless)-mobile

    • Haha sh*t up dude, this is Continuity and it’s by Apple… But only T-mobile support it yet in the USA
      Please DO YOUR research before arguing !

  2. I wonder if you can have 2 different phones, same phone #, and only have that count as one line on your account. I’ve always been an iPhone user but wouldn’t mind picking up a cheaper Android phone to fool around with once in a while.

    • Josh Lambert - 7 years ago


    • Grayson Mixon - 7 years ago

      On Verizon, each phone on an account has an additional $20 access fee. It could work the same way, but with a smaller fee. Say, $20 access fee for a new line. $10 access for an additional device using the same line. Something like that might work.

  3. bpmajesty - 7 years ago


  4. this is designed more for the sim card enabled smart watches and tablets than another phone, but it might work that way too.
    This is network level number duplication, vs Service level replication, which is what the iCloud solution is. iCloud solution requires your phone to be on and connected to the ATT network and able to talk to the iCloud servers.
    This solution will not require that your phone even be on, as it pretty much duplicates the SIM info on multiple SIM cards.

  5. Peter W. Alt (@pewalt) - 7 years ago

    This has been around in Europe for years and in personal experience it never worked reliably. But yay for putting a new flashy name on it and finally introducing it to the US market.

  6. dereth - 7 years ago

    WHAT? We already have multi-SIM plans all over the world with other carriers.

    I’m holding on to a multi-SIM from Singapore’s SingTel since 10 years ago when I was rocking a BlackBerry and a regular Sony Ericsson phone. (They were UNLOCKED even then, LOCKING phones was a concept that only exist in US and Japan.)

    Same line, different devices.

    You can even punch in a standard set of codes and select your preferred device to receive incoming phone calls and SMSes.

    I’m still using the same combination on my Samsung S5, iPad, and Nvidia Shield Tablet. (Still unlock. All of them. Most people outside of US have never even heard of phone locking)

    3 sims, 1 line. One shared voice and data plan for all devices.

    American carriers took this long?

    Seriously, you’re all royally screwed by such companies.

    NOTE: Oh… and before the iPhone came about, we were already able to tether the data connection on our phone for FREE. YES. Free as in beer. No extra charges.

    • Grayson Mixon - 7 years ago

      “You can even punch in a standard set of codes and select your preferred device to receive incoming phone calls and SMSes.”

      Apparently you missed the point of the article. There is no preferred device. It works equally on all devices, all the time. You don’t have switch between devices.

      Responses like this make me question what the truth is when people say they’ve had something for years. When you dig down, it’s not actually the same.

      • dereth - 7 years ago

        Data works across all devices.

        IF, and IF… you prefer, you can route your calls to just one device. Calls and SMSes only. Or whatever it is called in US that differs from the rest of the world.

        Data will work simultaneously across all your devices.

        As the article said, “The goal is to let you send and receive phone calls or messages from all your connected devices without relying on a specific app or operating system feature.”.

        I did not get to realise how restrictive US carriers were until I was given the charge of managing global mobile communications for my company a decade ago.

        Some of the global carriers I had to work with From 16 countries include AT&T, Verizon, SK Telecoms, China Mobile, NTT Docomo, Telecom Italia, Telekom Malaysia… just to name a few.

        That was when I had to work on contractual agreements with them and boy was that a culture shock.

        Notable examples includes learning about device locking in Japan and US. How apps were restricted by US carriers (Verizon Navigator anyone? LOL), no tethering, no multiple devices tied to one number, no roaming voice plans…

        And one more interesting point that got me really confused but amused at the start… :)

        Any plan or value added services termed “World” does not mean that the service extends to the rest of the world, such as voice calls while you are traveling somewhere in Asia. It just means you are able to use your phone across the 50 states.

        To anyone outside of the US, it was a novel concept on “world”. :)

        I was placed in a position for years to see the overall (global) picture from a unique vantage point and learned some interesting facts with regards to mobile communications.

        So… well, yeah. You can’t obviously believe everything you hear on the Internet.

        I’m just sharing my humble experience. :)

  7. Terrence Newton - 7 years ago

    I feel like this technology will overlook a large issue that Apple’s Continuity feature does address. If I’m using my Mac and I get a text message, it will pop up on my screen first, and the notification on my phone will be delayed by maybe half a minute on my iPhone. That way, I don’t have notifications going off on all my devices every time I get a message. It shows up first on the device I’m currently using. Also, reading a message on my Mac marks it as read on my iPhone and any other devices as well. Yes, obviously Apple’s Continuity won’t work with non-Apple devices, but I still believe it’s the best implementation of such a feature.

    • staaaaaan - 7 years ago

      I think this is to be in support of the recent cellular Continuity feaure, while at the same time catering to other devices

  8. Oflife - 7 years ago

    Or wait for Pi from a company in the UK. Future proof. Decades in the planning. One number, for life.

  9. Craig Hart - 7 years ago

    Will this allow me to connect a cellular iPad to my mobile share plan without having to pay an extra monthly fee?


Avatar for Zac Hall Zac Hall

Zac covers Apple news for 9to5Mac and hosts the 9to5Mac Happy Hour and 9to5Mac Watch Time podcasts.