iPhone XS and Dual SIMs


With the launch of iOS 12.1 comes the feature I was most excited about with this year’s iOS update – Dual SIM support. This means I can have not one but two cell carriers active on my phone at a time through the use of eSIM cards. Most people are famaliar with SIM cards in their phones, the little chip from the carrier that identifies you to the network. And this is an electronic version of that. As someone who’s always had a fascination with the cellular industry and technologies powering the industry, this would be my first time to have two carriers on my daily driver, and a dream come true. I mean – double the speed tests!! This hardware feature is included in this year’s iPhone XS, iPhone XS Max, and iPhone XR.

For the first 30ish years of my life, I lived in Texas where AT&T is amazing. A couple years ago, I moved to Seattle and while no carrier is great, Verizon is the best option and my carrier of choice for the past couple years. I’ve also noticed that Verizon is not great in Las Vegas where I sometimes travel for work. With a few trips coming up in places with different “best options” for carriers (Texas, Vegas, NYC, San Diego) it seemed like a great time to give dual SIM a try.


A few nights ago, before the public release, I downloaded the beta of iOS 12.1, then went into an AT&T company-owned retail store the next morning. The rep was clueless when I mentioned I wanted to activate an eSIM. I clarified that they have blue eSIM cards with QR codes on them in-stock (I knew this from online research) and that I wanted to add a new line of service if he was willing to go through the process. It was a gross add (new line of service), so of course he was. I had to re-clarify as well that I was not porting my Verizon number, but instead I wanted a new number and would have both on my phone. He seemed a tad confused at first, but that was to be expected.

He grabbed the eSIM card from their backroom, and I grabbed the second IMEI from Settings -> General -> About (under your main carrier). My iPhone XS was purchased on the Apple Upgrade Program, so it’s completely unlocked. He activated the line just like normal, using the ICCID from the eSIM card and the IMEI I provided. Once he was done, I went to Settings -> Cellular -> Add Data Plan and scanned the QR code, but activation failed. I wondered if a data connection was needed and connected to Wi-Fi as Verizon is dead in their store (basement of a mall downtown). The second time I scanned the code, with some of the store staff watching, I got a confirmation that asked if I wanted to add the AT&T cellular plan to my phone. I confirmed, and it took about 90 seconds for the device to communicate to the network and activate followed by a quick prompt to select labels for each line and the default voice and data lines. Apple suggests some labels such as Business/Personal/Primary/Secondary, but you can also use custom labels. I went with “AT&T” and “VZW”.

(As a side note, I will eventually swap the services on SIMs. I want Verizon on my eSIM, as they’ll likely remain my primary carrier, and then have AT&T on the physical SIM so that I can remove and add an international or other carrier’s SIM in the future.)

How It Works

The technology Apple uses for dual SIM support is called Dual Sim Dual Standby (DCDS), which means that both lines are active when in standby mode, but when you connect a phone call, the other line becomes inactive and will not transmit calls, text, or data.

I have Verizon setup as my primary voice and data lines and switch the data carrier as reception dictates. In the Setup menu, once both lines are active, you can easily make this switch.

The Catch

All signals are not created equal! Currently the iPhone will not maintain two LTE connections, even if both carriers support it. The line you’ve selected to be your data line will maintain the best connection possible (LTE then fallback to HSPA), but the secondary line will revert to CDMA in the case of Verizon and HSPA in the case of AT&T. What does this mean?

With a CDMA carrier (Verizon) as both your primary data and voice lines, if you get a call on HSPA (AT&T), then AT&T will become active and you can use simultaneous voice and data over HSPA, and the secondary carrier is completely offline. Also with this setup, any calls or data connections over the CDMA carrier function just as if the CDMA carrier was the only carrier on your phone.

If your HSPA carrier is the primary data line, it will likely have an LTE connection, but the CDMA carrier will only maintain a CDMA connection, not LTE. This poses a problem for Verizon as currently it’s estimated that 20% of their network is LTE only. Verizon has already said there’s something in the works for this, and until they’re able to “deliver Verizon’s full suite of voice and high-speed data services, [they] won’t activate Verizon service on any eSIM.”

The one time where this became an issue was when I needed to make a call to a financial institution, and I decided to use the AT&T line to make a voice call. However the financial institution wanted to send me a text on the Verizon number, which I couldn’t receive while on the phone. Something to beware of in the future!

Battery life

As I was anxiously awaiting the ability to give dual SIM a try, I was contemplating battery life, and I’m happy to say that I’ve been using dual SIM for about 5 days now and don’t notice any difference in battery life. With DCDS the phone is checking in with each provider at separate intervals and not maintaining two active connections at once to help alleviate battery issues.

Carrier Support

At the iPhone keynote, Verizon, AT&T, and T-Mobile were announced as carrier launch partners, and it’s reported that Sprint has since confirmed that it will support eSIM as well. However with the launch of iOS 12.1 all three launch partners have said they’re not quite ready and will be launching sometime in the future. Apple does maintain a list of all the international carriers that support eSIM.

Recovering Texan proudly in the PNW. Cyclist. Avid traveler and aviation geek. Apple fanboy. Lover of cold brew. Maker of SassTags. Learning Python. he/him. ⚣

Site Footer