Sorry, not the topic here, but now that I get a better view of how VoLTE is working, I think this sentence is incorrect. To work, on Qualcomm SoC, VoLTE requires the following:
- a
mbnfile provided by Qualcomm. It contains the configuration for the modem to handle VoLTE as implemented by the network providers. So actually, this file is designed by the providers themselves, with Qualcomm engineers, for their setup. There is a (very) long list of parameters, including for instance how to handle SMS when using the IMS for VoLTE… One wrong value on a parameter and it’s not working. Of course, it’s SoC dependant, in addition to being network provider dependant. - a link in OEM partition, provided by Sony, that associate the service ID of your provider to the right
mbnfile. - a oFono plugin to allow to talk to the modem via the IMS stack.
- a bit of middleware to switch from classical GSM stack to the IMS one.
Obviously, Jolla implemented 4., and created also 3. (closed source ;…( but I didn’t notice bugs there). Jolla developpers helped Sony with 2., with the help of the community to associate service ID to mbn files. So far, there is no issues related to these points. But remains point 1. And this, no one can do anything about it except the network providers and Qualcomm. There is no documentaion on the Internet, only very few resources to parse and generate mbn blob files. And there are many, many parameters, all of them undocumented with arbitrary values like 1, 3, 7… Guess what they mean.
If you have a good mbn file, VoLTE is working quite well. If you don’t, you may have voice but no SMS, you may have phone calls but no voice… I’m afraid Jolla did their maximum on that topic: middleware and modem access. The issues are in the implementation of VoLTE in the modem. It requires too many parameters that are out of reach if you’re not a Qualcomm engineer working with a network provider engineer.