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Comment by DoofusOfDeath | Hacker News Reader

Can someone help me understand the relationship between phone hardware and carriers in the US?

I recently bought a new, unlocked Samsung phone on Amazon. When I put a Verizon SIM card into it, a Verizon-specific firmware module got added. I don't understand why that would be necessary.

Asking because I'm attracted to the idea of a phone I truly control, but not sure what that means for carrier compatibility.

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T-Mobile and Verizon should allow any modern device. Verizon used to need a activation conponent for the CDMA radio but modern devices just use LTE and voLTE. They did have a visual voicemail blob that used to be pulled in, but now they follow spec and don't require anything special.

Sprint (which is now T-Mobile) has required an activation app for their CDMA devices called SprintDM. Without it, phone will not activate and work. Most alternative OS like LineageOS don't include it, but if you activate on stock OS and don't wipe modem partitions, it continues to work. Thankfully they are transitioning to T-Mobile network.

AT&T has no activation crap but may not let imported devices based on IMEI numbers they don't have.

In Europe, GSM is still being used. I heard in they are being phased out. Anyone knows how that will affect old nokia type of phones?

The cheapest candy bar phones available started having 3rd gen (WCDMA) network support around 2010, so GSM-only handsets should be out of active use. Of course the classic monochrome Nokia phones will cease working once GSM is shut down.

On the other hand there must be quite a lot of embedded devices using only GSM. For example, this year the elevator maintenance company offered our housing company GSM emergency phone units to replace landline-based ones. WCDMA-supported units would have cost a few thousand euros more.

This is the correct answer as I can attest to one of my phones pulling down a visual voicemail blob and also a problem I had with a Sprint based CDMA device that was running Lineage OS that lost cell connection and I could not get it back without flashing back to the original ROM. (Thanks for posting this @joecool1029 and confirming what I was witnessing)

Once AT&T goes VoLTE only they're going to have a limited list of accepted phones. sigh

I still remember being at RadioShack and glancing at the Verizon section and thinking "hey, it's the island of misfit phones!"

Not sure how helpful this is, but I know that Verizon requires some kind of special sauce that the other GSM carriers do not.

I got a Verizon SIM recently and it would not work in my iPhone 8, which I bought in Germany. Fortunately the salesperson thought to ask if it was a foreign phone! Turns out Apple only sells the Verizon-compatible phones in the US, but doesn't exactly broadcast that fact elsewhere.

The Android (or Linux) situation is probably different in the details, but not in principle.

> Asking because I'm attracted to the idea of a phone I truly control, but not sure what that means for carrier compatibility.

I haven't looked in a while but IMO if you want this, the only feasible way is likely to go with carrying an internet hotspot and off-shoring 2/3/4G functionality. Ideally, a phone without the second processor is the only way to actually achieve this -- then you have "only" the chip hardware and wifi chips to deal with/secure.

I used 3 different unlocked phones in US, as for US sim cards, I used MetroPCS, T-mobile, and Cricket, non of those added anything, althought their respective websites told me about an app they strongly reccomended. Only trace was the Sim card toolkit menu which was diaplayed for whatever inserted sim card, but I never used any of those.

Depending on the device you are using you might not have noticed.

I used WireShark on a hotspot that my unlocked IPhone was using and captured the visual voicemail blob used by Cricket/AT&T just last week.

Also, the SIM card toolkit can be used remotely by your provider. Lookup SimBad exploit

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