VoLTE / IMS explainer (unrelated to Samsung)
Wikipedia has a good graph explaining how LTE relates to 4G. VoLTE is a collection of technologies that get reused in sucessors. The less market-y term to use is IMS as that is what your devices IMS stack interfaces with at the carrier past some gateways.
The underlying transport isn’t essential to what VoLTE or VoWifi is. It’s regular SIP at the core behind more carrier acronyms (ePDG, P-CSCF).
Even if you technically interface with the IMS, after authentication the gateways can say “yes” or “no” to your particular IMEI that implicitly tells the device model (or by its user-agent).
Certification might mean carriers making sure your device and IMS implementation meet some criteria (on 911 emergency calls, audio codecs it wants etc).
To even get to your carriers IMS, the smartphone needs to ship an implementation and that is what’s missing on (older?) exynos Samsung builds. Sony, Pixels, Motorolas etc do though, especially qualcomm based ones. For those, LineageOS added the warning to at least register once with the original firmware to get the IMEI allowlisted (but it isn’t strictly necessary in my experience).
All that said: screw carriers and their acronyms for voice. If you can, use the call function in messengers (webrtc mostly) or a dedicated SIP client (with cloud messaging notification). It adds latency to the call because they won’t be prioritized, but at least will use a highquality voice codec (Opus mostly). Family&Friends get the cue and call back the same way. Though I see the issue if you’re doing business on a phone number or the day comes when you need to call emergency services.
/explainer end
For builders of older Samsungs, one option is the “FLOSS IMS”(1) by phh. There’s also an integration into TrebleDroid GSIs. It’s prototypish and has mixed feedback (because very carrier dependant).
Then there’s a monkey patched proprietary Samsung IMS pakage (2) that builders can try to apply per device (Readme is good, also see “Shenanigans” section).
There are /e/OS GSI threads (A13 and A14) building up on TrebleDroid (3), you could ask there as to if (1) can be / is included and what’s the feedback.
- (1) GitHub - phhusson/ims + discussion
- (2) GitHub - jameskdev/android_samsung_imsservice: An attempt to enable IMS on samsung devices
- (3) GitHub - TrebleDroid/treble_experimentations: Scripts to automatically build/CI/Release TrebleDroid GSI
Murena is at least aware of the phh work (1). You could also ask in the weekly devel thread if this is tracked internally still for Samsungs.