Update 1 (5/8/19 @ 5:55 PM ET: The documentation uploaded for the Android Q beta 3 release confirms that carrier restrictions on multi-SIM devices has been added in the latest release.

It has been just a week since we put out an exclusive on the early build of Android Q. According to the build we've got, the latest iteration of the operating system includes some long-awaited features like system-wide proper dark mode, revamped and more detailed permissions controls, and more. But, every version of Android includes a feature nobody asked for. This time, it is much more serious than unwanted navigation gestures from Android Pie or the stark white interface from Android Oreo. Apparently, Google is going to let carriers use easier methods to SIM lock the devices.

9to5Google noticed four commits on the Android Open Source Project Gerrit about the changes. All of the commits are called "Carrier restriction enhancements for Android Q". 9to5Google reports that after looking at the sources, they could verify that Android Q will let carriers include a blacklist and whitelist of carriers. Starting from the soon-to-be-released version of Android, carriers will also be able to restrict the dual-SIM functionality of the device. They will be able to completely lock out the second SIM slot unless there is a verified (added in the whitelist by the carrier) SIM card in the first one.

I think this is the time to officially start recommending unlocked phones over the carrier-locked ones. True, they have good plans which sometimes sound too good to be true, but I think one shouldn't sacrifice bootloader, SIM slot, update speed, network reliability, hotspot capabilities, and many other features for just saving a buck. All these 'restriction enhancements' will definitely make it harder for developers to provide custom ROMs, kernels, and other kinds of mods for certain devices. As you know, unlocking the bootloader is mostly in connection to a SIM lock.

Android Q is still in the early days of development, so it's possible these features won't be present in the final build. We will keep an eye on things.

Via: 9to5Google

Source: AOSP Gerrit

Update 1: Added in Q Beta 3

New fields added in the TelephonyManager class, especially "MULTISIM_NOT_SUPPORTED_BY_CARRIER," confirm that Android supports carrier restrictions on multi SIM devices. The description for the aforementioned integer field states:

The usage of multiple SIM cards at the same time to register on the network (e.g. Dual Standby or Dual Active) is supported by the hardware, but restricted by the carrier.

We'll have to wait and see if this increases the frequency of multi SIM devices locked by carriers. Most devices sold in the US have a single SIM, so this could be a way for dual SIM devices to be sold by carriers while retaining control.