Google Fi Uses Dual SIMs in a Really Cool Way

Google's wireless carrier, Fi, will use the Pixel 4's dual-SIM capability in the coolest way possible: to connect to two US networks simultaneously and use whichever one works best.

The Google Pixel 4 has "dual SIM, dual standby" technology with one physical SIM and one eSIM. That can let you keep two lines on the device—one for home and one for work, for instance; or one for the US and one for international roaming. Fi's new trick uses both SIM slots to improve coverage.

One of Fi's key strengths has always been that it combines the Sprint, T-Mobile, and US Cellular networks for better coverage than you can get on any one of the three networks alone. But until now, that's relied on some network-based switching algorithms Fi users have often quibbled with. The general complaint is that the network tends to keep phones connected to Sprint even when T-Mobile is a better choice in the area. And when it switches networks, it can briefly drop its connection.

Well, now Google's taking this on-device. By using the phone's SIM card and eSIM slot at the same time, Google says Pixel 4 phones on Fi will connect to two networks at once (it's not saying which two out of the three, but it's usually Sprint and either T-Mobile or US Cellular.) The phone will then decide on-device when to swtch back and forth.

This falls slightly short of the absolute coolest way to use this technology, which would be combining both networks with something similar to Republic Wireless' "bonded calling" tech. But by keeping both networks live on a phone, switching will be quicker and more seamless, avoiding apparent connection drops as the device flips from one network to the other.

For now, this feature will only work on the Pixel 4, but Google promises to "expand dual connect technology to more Designed for Fi devices." That's interesting, as the Pixel 3a and 3a XL are the only other devices in Google's Fi lineup with the DSDS technology necessary to make this work. Is Google just talking about those, or does it see more coming down the pike? We'll see.

About Our Expert

Sascha Segan

Former Lead Analyst, Mobile

My Experience

I'm that 5G guy. I've actually been here for every "G." I reviewed well over a thousand products during 18 years working full-time at PCMag.com, including every generation of the iPhone and the Samsung Galaxy S. I also wrote a weekly newsletter, Fully Mobilized, where I obsessed about phones and networks.

My Areas of Expertise

US and Canadian mobile networks
Mobile phones released in the US
iPads, Android tablets, and ebook readers
Mobile hotspots
Big data features such as Fastest Mobile Networks and Best Work-From-Home Cities

The Technology I Use

Being cross-platform is critical for someone in my position. In the US, the mobile world is split pretty cleanly between iOS and Android. So I think it's really important to have Apple, Android and Windows devices all in my daily orbit.

I use a Lenovo ThinkPad Carbon X1 for work and a 2021 Apple MacBook Pro for personal use. My current phone is a Samsung Galaxy S21 Ultra, although I'm probably going to move to an Android foldable. Most of my writing is either in Microsoft OneNote or a free notepad app called Notepad++. Number crunching, which I do often for those big data stories, is via Microsoft Excel, DataGrip for MySQL, and Tableau.

In terms of apps and cloud services, I use both Google Drive and Microsoft OneDrive heavily, although I also have iCloud because of the three Macs and three iPads in our house. I subscribe to way too many streaming services.

My primary tablet is a 12.9-inch, 2020-model Apple iPad Pro. When I want to read a book, I've got a 2018-model flat-front Amazon Kindle Paperwhite. My home smart speakers run Google Home, and I watch a TCL Roku TV. And Verizon Fios keeps me connected at home.

My first computer was an Atari 800 and my first cell phone was a Qualcomm Thin Phone. I still have very fond feelings about both of them.

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