Additionally, if you are looking into a particular device's compatibility on a network, see if the phone has a dedicated page on the subject before reading this page as compatibility may differ by device.
This page is for general information on various carriers and their MVNO's in regards to their compatibility with Garaho phones.
Some carriers employee whitelists for using VoLTE (4G phone calls), which can cause a non whitelisted phones to not be able to make calls. This and other carrier specific information may be found on this page.
Some carriers have strict phone specific whitelisting for the registration of IMS. Without IMS VoLTE will not work. VoLTE is how calls function over a 4G network and so with many countries undergoing a 3G shutdown some carriers no longer support calls at all on some devices.
Currently in Canada 3G is being phased out, with some carriers already having phased it out of their networks, and the rest are in the process of doing so1.
Telus and their MVNO's do not seem to have a whitelist in place, and IMS has been found to be registered on the A202KC2.
Rogers and Fido are generally known to have a whitelist in place for IMS registration3. The A20XKC4 and KY-4XC5 do not seem to be on the VoLTE whitelist6. However the 90XKC seems to be able to register for IMS7. This may be due to SoC differences.
Bell does not seem to have an IMS registration whitelist8.
Does not seem to have a whitelist, needs further research.
Notably, users of the KY-42C have been able to receive updates through T-Mobile and it's subsidiaries9.
Needs expanding, see: https://www.reddit.com/r/dumbphones/comments/1kalghp/japanese_flip_phoneskeitais_australia/