Android 14 QPR may bring "virtual" dual SIM active support to Pixel

While I personally only use a single phone line when I'm not traveling*, I know many people use two (or more) lines on a daily basis. Some keep multiple lines so they can have one for personal contacts and one for work contacts, while others do it because they can save money by mixing and matching plans from different carriers. Juggling multiple lines can be a challenge, but fortunately, Android lets you choose which SIM to use as the default for calls, texts, and data. Because of hardware limitations, however, Android doesn't let you use one SIM for mobile data while another SIM is in the middle of a phone call. Google might have a solution to that, though.

Many mobile phones, including Google's Pixel devices, support dual SIM dual standby (DSDS). Phones with DSDS support can only have a single active cellular connection, meaning that only one SIM can be actively used for calls, texts, or mobile data, as the other SIM is put in "standby". This means that if you want to use mobile data while in the middle of a phone call, the same SIM you're using for phone calls has to also be used for mobile data. 

As I mentioned before, many people mix and match plans to save money. Say you have a phone that supports DSDS where SIM 1 from carrier X is used only for phone calls and texts while SIM 2 from carrier Y is used only for mobile data. In this scenario, you wouldn't be able to place a phone call over VoLTE/VoNR through carrier X while using carrier Y's 4G/5G network, meaning you wouldn't be able to look up anything on the web while you're in the middle of a phone call**.

Phones that support dual SIM dual active (DSDA), however, don't have this problem, as they're able to have two concurrent cellular connections. Whether a phone supports DSDS or DSDA is typically determined by its hardware, however, as maintaining an additional cellular connection requires having a second modem. Many phone makers don't include a second modem because it requires additional space, raises the price, and reduces the battery life to cater to a relatively small number of users in the grand scheme of things.

That's where a new feature called virtual DSDA may come into play. In the Android 14 betas, there's a configuration called "config_enable_virtual_dsda" (emphasis mine). I spotted this a while back but only recently have come to better understand what it's for. This flag, when enabled, should allow for both SIM subscriptions on the device to provide data while in-call even if the device only has a single modem. This is my educated guess based on the name of the flag, however, as this config isn't referenced anywhere else in current Android 14 builds, not even in the telephony framework. 

The flag is currently set to false by default, and there are no overlays overriding the value to true on any current Pixel. However, I've heard from a source that this feature is being worked on, and I have reason to believe it could be limited to the Pixel 7 and later. I don't know if the feature will launch with Android 14 QPR1 or if we'll have to wait for QPR2 or later, however. 

As for how exactly this will work and why I'm expecting it to only work on the Pixel 7 series and later, I believe it's because only the Pixel 7's radio software is set up to support the "logical" modem stack that is necessary for virtual DSDA to work. This, by the way, is how the Pixel 7 is capable of supporting dual eSIM (eSIM MEP) even though it only has a single physical eSIM chip. Hopefully I'll find more clues about this feature in the upcoming Android 14 QPR1 beta!

* In case you're curious, Red Bull Mobile is a real MVNO. Yes, I too was surprised to learn it's real. There was a deal that would give you 1GB of data for a year for free, so I took it because I needed more eSIM lines to test upcoming eSIM-related features.

** A feature called "backup calling" (Pixel) or "auto data switching" (Samsung) allows for using the mobile data connection from one SIM to enable calls/texts from the other SIM over VoWiFi. This requires that the carrier supports VoWiFi, allows this feature to be used, and also allowlists the device to use VoWiFi.