US carriers are only just acquiescing the concept of eSIM after much begrudging and skirting of the rules. But having an eSIM on-board a phone brings the potential of dual-SIM functionality with just one physical SIM slot.
However, we’ve only seen a couple of implementations so far: Single Standby, where only one SIM card is used at a time for any purpose, and Dual Standby, where one SIM accesses data, but both can take and make calls and SMS.
Sorry for the confusion, our previous message should have stated you cannot use the physical SIM network and the eSIM network simultaneously. Appreciate your understanding.
— Made by Google (@madebygoogle) October 10, 2018
We’ve seen only Single Standby in use on the Pixel 2 and Pixel 3 series of devices, both technically dual-SIM phones with an eSIM and a card slot. But according to XDA-Developers‘s interpretation of new Android Open Source Project code, we could possibly see the Pixel 4 adopt a new dual-SIM configuration where both cards can be used for data, calls and texts: Dual Active.
It would ultimately take a second set of data radios to have both SIMs fully working simultaneously, but it seems that commit messages are using language that imply Google’s definition of a true “dual SIM mode” as either Dual Standby or Dual Active support.
The boolean is required to differentiate 2018 Pixel (which has 2 SIM cards, but dual SIM functionality is restricted to dog fooding) from 2019 Pixel (which will have dual SIM functionality) […]
In general, some devices will be single SIM, even if they contain two SIM cards, as the Pixel 2018 case and that is a valid configuration.
At the very least, being able to take calls and messages from both available phone numbers would be a good start for travelers. At best, the Pixel 4 could bond two cellular connections to gain stronger download and upload speeds.
But let’s remind ourselves that Android Q is poised to impose new carrier-locking options for dual-SIM functionality, so don’t hope for too much.