When the Pixel 6 (and other Pixel models) are used in China (regardless of whether the stock ROM or GrapheneOS is used), VoLTE calling does not work by default. Calling on China Unicom, the "budget" carrier in China, will at least work, but the connection will be automatically degraded to 3G. For China Mobile, it will be degraded to 2G, and for China Telecom, which is the carrier I use, it will not work at all, and SMSes can't be received at all either, which might cause some first-time users to believe that the phone's hardware does not have the capability to connect to China Telecom's network. However, there is a fairly easy way to enable this (in either the stock ROM or GrapheneOS) without rooting the phone by downloading two open-source apps, Shizuku and Pixel IMS, then using Pixel IMS to forcefully enable VoLTE. I can confirm that these steps work on a China Telecom SIM card issued in 2023. You can see a text guide here (based on the guide, apparently it is required for some Korean carriers too), and watch a video of the process in Chinese on Bilibili here. Is it possible that such functionality to enable VoLTE be added to GrapheneOS by default so China Telecom SIM cards work on a fresh install of GrapheneOS? Thanks!