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>And if you have a modern enough SIM+phone combo, it won’t even display the 2g network as an available network, nor 3G on my device.

Source? It might just be that your carrier retired its 2g/3g network, not that the phone/sim refuses 2g/3g connections. If some cell tower popped up claiming to 2g/3g, your phone still might happily connect.

by Scoundreller12 hours ago|

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source = Rogers SIM in me phone

my Telus/Bell SIM shows the 3G network tho

by lxgr2 hours ago|

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Unfortunately, I think there's no way for a SIM card to indicate to the phone that it would like it to please never connect to any 2G (or any non-mutually-authenticated) network.

Absent that, maybe this happens via a carrier profile (or equivalent mechanism)?

by Scoundreller29 minutes ago|

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Ah, so the attack might depend on whether your phone is set to allow roaming or not. Maybe.

But I only have an option for data roaming on/off, not roaming entirely.

by lxgr20 minutes ago|

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I don't think that matters, since the phone has no way of knowing from the SIM card alone whether it should still connect to 2G networks or not.

It sounds like a good idea to at least restrict 2G connections to non-roaming scenarios, but then you have the next practical problem: How does your baseband know that you're abroad?

Sure, all solvable at the application layer (the phone could use location heuristics to figure out where it is etc.), but not trivial and full of edge cases that could easily result in your phone mysteriously not connecting while abroad or, worse, not being able to make an emergency call or similar.