Apple appeared to become the exception due to having such an "in-demand" handset (going exclusive with AT&T initially might have helped them negotiate better terms with other carriers to get the iPhone to their networks) - mobile operators can't modify the iOS firmware at all. On any other phone, expect branding, pre-installed bloatware apps, modified startup and shutdown screens, modified top-bar to show "5G" on presence of a 4G network, and 6+ month delays to security updates while they get the above modifications made to the firmware before they approve it.
Arguably part of the "control" mindset comes from CDMA networks, where you couldn't "pop the SIM" and change network - you had to get the ESN whitelisted on the network, and that gave the carrier a lot of control over your ability to switch phone, or whether you could buy it from anywhere except themselves. I guess GSM carriers admired this level of customer-capture, and wanted to replicate it.
It sounds like "GSM" carriers are going to have to move fully towards whitelisting to preserve voice calling service when they get rid of their circuit switched fallback networks.
Inbound roaming of foreign users will be interesting in the next few years - without any CSFB voice support, they will likely not be able to serve most incoming roamers (who don't have network-to-network arrangement for VoLTE roaming), and that might cause a loss of roaming revenues once travel levels return towards more of a normal.
https://www.apple.com/newsroom/2007/01/09Apple-Chooses-Cingu...
Have never seen anything like that on Pixel / Nexus phones bought from Play Store and not tied to a particular network. Is this an issue specific to carrier-bought phones or are all Pixels exempt?
None of that applies if you buy a phone separately from the carrier (so Google phones, or OnePlus, or similar), but most of those also make arrangements with the carriers, I think, to recognize the phone before sale (at least, my carrier recognized both my Pixel and OnePlus devices at the times I had them).
Apple was the exception because they initially went with AT&T. Jobs demanded no carrier interference. The first carrier they approached (Verizon, IIRC?) refused Jobs' demand, so instead of caving, Jobs went with another carrier.
It's an eerie feeling finding errors or omissions in what is commonly used as an irrefutable source of truth in the modern world. I appreciate the correction though!
Perhaps irrefutable is too strong a word, but if I'm looking for an answer (instead of researching a topic) and want a quick, single source, Wikipedia is my go-to.
Why? Isn't that stuff they run in software (on network hardware) and could emulate forever for a low cost? (Or at least for another decade until very, very few people would care.)
There's also a lot of implications of moving CSFB type functions into the IT environment due to completely different security assumptions in both worlds.
That's not to say you can't do it, but the circuit switched networks are very often actual literal networks of legacy hardware that operators want to get rid of and take out of service.
The cost of keeping legacy systems going is also raised due to skills shortages and limited expertise. Another reason operators will try to get rid of it if possible.