Xiaomi 13

syaoran wrote:

Android uses profiles that aren't accessible through the OS through normal means, when possible, for a specific implementation of VoLTE, WiFi Calling, and VoNR.  Different carriers have different implementations, making the devices more carrier specific or more region specific.  Asian implantations of VoLTE, VoNR, and WiFi Calling are not normally compatible with EU and North American regions.  This is a carrier.choice. 

T-Mobile USA, T-Mobile, and EE as an example, use the same implantation.  AT&T USA's implantation is not compatible with T-Mobile's, which makes it harder to use a non-AT&T device on their network.  Asia has a more proprietary implementation that is focused towards the market those devices are made for and designed to work in.  If they were to use the stock Android implementation that T-Mobile uses, VoLTE, VoNR, and WiFi calling would not work on Asian carriers.  

There are tutorials out there  including on the official Xiaomi boards on how to alter the carrier profile using root.  The issue with that is, that the profile resets to what it originally was every time the device is rebooted or updated.  Qualcomm's QPST is the only way to properly set this, but it is not a user friendly tool and can easily brick your device or cause it to no longer be able to connect to any networks.  The way the tool works is by writing to the oartition of the device where the modem firmware and configuration is stored, which is outside of the OS.  If this gets messed uo, a factory reset will not restore it!  This is why I don't talk about it much.   

I used a Motorola phone I bought in the US for 4 years in India, so is the interregional implementation incompatibility only one-way? Phones from the US will work universally but not the other way around? You also say that Asia's proprietary implementation, if configurable to the stock android implementation necessary for US networks, would no longer work on Asian carriers, but that goes back to my question of how do phones from the US work fine abroad? Also how does international roaming work then if network configuration is device specific?