An interesting read about living life without any SIM card inserted into their smartphone:
https://blog.thenewoil.org/life-without-a-sim-card
Nates also links in the article about two good videos worth watching.
I do agree that’s a problem nowadays that, just by having a SIM inside your smartphone, it pings constantly to nearby towers. This can then lead to what’s called “triangulation”:
https://ssd.eff.org/module/mobile-phones-location-tracking#mobile-signal-tracking-towers
One thing that I can summarize from this, according to your own “threat model” or security plan (as the term used by the EFF), is to:
- Turn off Airplane mode, Wi-Fi and Bluetooth completely when not in use.
- Remove your SIM card from your main smartphone. In some regions, there are alternatives such as VoIP phone numbers that can be used instead, in combination with a SIP mobile client app. Some individuals like Naomi (from NBTV Media) uses Calyx Mobile Hotspot.