p1xel_p0etry GPS, phone's IMEI, OS version perhaps, information about texts or calls like frequency possibly.
The main difference is that, at least in the country I live. It is very hard to get a SIM card that is not linked to your identity. And when you use it in your phone, the identity gets linked to the device immediately. Even if I use the ESIM with a phone plan that is linked to my identity on my hotspot device. My identity is linked to the IMEI of the hotspot device which at this point, it already is. And when connecting the phone to the hotspot via wifi, the phone remains unlinked to my identity. I hope that makes some sense.
What privacy benefits are you gaining by carrying around a cellular hotspot linked to your identity while connecting to it using a phone unlinked to your identity?
Some GrapheneOS users keep their devices anonymous by not associating their device (and IMEI) with their identity. One main reason this is done is to prevent linking a user's location activity (through cellular tracking) with their true identity. The goal is to make it difficult to answer these two questions:
- What has Person ABC's location activity looked like over some time period?
- A cellular device was connected to a cellular tower at a specific point in time. Who is the owner of that device?
With your current setup, it's easy for some entities (such as a cellular carrier) to answer both of these questions. This is because you are carrying a mobile hotspot tied to your government identity that is continuously connected to cellular towers.
Depending on your threat model, this may not be a problem. Many GrapheneOS users purchase a phone using a credit card, set up the phone at their home, establish cellular service using their true identity, never turn on airplane mode, etc. They don't even consider the topics discussed in this thread. And there's nothing inherently wrong with that for users that don't feel a need to achieve "extreme privacy".
In your case, you're carrying a non-private cellular device already. I don't mean to discourage you, but going through obstacles to keep your GrapheneOS "anonymous" may not be adding much privacy benefit for cellular tracking specifically. There's nothing wrong with doing so of course, if you don't mind the inconveniences. For example, maybe there is a possibility you'd like to later establish a private cellular subscription and migrate away from the nonprivate hotspot.