My recommendation would be to purchase a GL 750 travel router (mudi) and install Blue Merle software (2 commands). You can then switch the IMEI every time you switch the sim (ie, monthly) so the most you would typically reveal would be a months worth of tracking data. Also, 100% of your traffic will be over VPN so the provider will know nothing about your browsing habits / destinations. And Blue Merle will also wipe the connection logs from the router.

If you want further clarification this is actually true: Airplane mode on phones turn the cellular radio off completely but having a SIM would still let you use over-IP carrier services like WiFi Calling. Send an SMS to yourself when you have Airplane mode on, you will receive it. Just not having a SIM isn't enough, you need to have both no SIM and airplane mode because it will broadcast to allow calling 911. The new Pixel Tablet has no cellular radio if you want to completely avoid it.