Before installing GrapheneOS, a Pixel phone must first boot with stock Android to connect to the internet to enable OEM unlocking. It's not possible to enable airplane mode to turn off cell radios before this first boot. Airplane mode can only be enabled after the first boot and after answering the initial Android setup questions.
If this boot process is completed without ever inserting a SIM card and over a wifi connection, are any cell identifiers like IMEI leaked to cell carriers or towers? I wonder if this first boot could leak the location of first boot to nearby cell towers and carriers.
I haven't been able to find details on what interactions cell phones have with cell towers even when a SIM card is not present. In this case with stock Android on first boot, are there any IMEI-leaking interactions such as preparation for 911 calls, time syncing, determining which basebands are available, etc?
If someone wants to avoid leaking a particular location (such as their home) with IMEI, should they perform the first Android boot in a remote location and immediately turn on airplane mode? Maybe even the GrapheneOS installation should be done in a remote location as well?
Similarly, the first boot after installing GrapheneOS happens with airplane mode disabled. Does the first boot on GrapheneOS without a SIM card leak anything to cell towers before airplane mode can be enabled? The documentation doesn't discuss this case.
I'm not worried about the wifi part since there are ways to limit the privacy leaks (like VPN configured on router to hide IP address). This discussion is kind of related but it doesn't talk about the cellular details when a SIM card isn't inserted.