(Credit: T-Mobile)

T-Mobile subscribers with the right type of iPhone can now add a second number using the carrier's new eSIM app.

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Available in the App Store, the T-Mobile eSIM app marks the carrier's official support of Apple's dual-SIM service. Through the app, T-Mobile customers who own an unlocked iPhone XS, iPhone XS Max or iPhone XR can add a secondary line to their device by choosing a prepaid plan. In addition to having a supported iPhone, you must be running iOS 12.1.1 or higher to set up the eSIM service.

eSIM is Apple's novel way of supporting a second line on the same phone. Instead of requiring two physical SIM cards, eSIM uses a built-in digital SIM so you can maintain two phone numbers. Juggling two numbers on the same phone can be an asset to people who travel to other countries or need to keep separate lines for home and business. eSIM is accessible only on the iPhone XR, iPhone XS and iPhone XS Max.

Verizon Wireless and AT&T also support eSIM. Like T-Mobile, Verizon lets you set up the service through an app, but it's available only for new customers. Existing customers still must call Verizon or visit a nearby store to set up eSIM. AT&T requires you to scan a QR code to activate eSIM. The major limitation with T-Mobile's service is that it's limited to prepaid customers, though the company said it plans to support postpaid plans in the future.

Using the app, T-Mobile customers enter an email address and follow the steps to activate eSIM. You're then asked to choose one of three supported prepaid plans (note that the expiry date refers to the amount of time you have until you must refill your prepaid account):

  • T-Mobile ONE Prepaid with unlimited voice, text and data for $70; 30 day expiry.
  • Simply Prepaid with unlimited voice, text and 10GB of LTE data for $40; 30 day expiry.
  • Tourist Plan with 1000 minutes, unlimited text and 2GB of LTE data for $30; 21 day expiry.

T-Mobile's new eSIM activation leaves Sprint as the only one of the four major US wireless carriers that still doesn't support the dual-SIM service.

As another development in the eSIM saga, Apple has released iOS 12.1.2 for iPhones. The latest iOS update carries bug fixes for eSIM activation. If you bump into trouble setting up eSIM with your carrier, download this new update and try again.

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  1. T-Mobile now lets customers activate Apple's dual-SIM eSIM service through a new, dedicated iOS app.
  2. eSIM is available only to T-Mobile prepaid customers, though the carrier plans to support postpaid plans in the future.

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Lance Whitney is a freelance technology writer and trainer and a former IT professional. He's written for Time, CNET, PCMag, and several other publications. He's the author of two tech books - "Windows 8 Five Minutes at a Time" and "Teach Yourself VISUALLY LinkedIn."