Currently supported devices are Redmi Note 9 Pro Max, Mi10,Mi10T, POCOX3, Redmi Note 9 Pro, Redmi Note 9, Redmi Note 7 Pro, Redmi8A Dual, One plus Nord and One plus 8T along with iPhone.
This seems to be testing with some most popular phones, list may grow like it happened with Airtel, remember even Airtel had very limited supported phone but now almost all Mobile running Android 9 and 10 are supported.
They have infact more phones VoLTE supported than Airtel. (only by slight margin). It's still a beta and updates have to be pushed by OEMs not Vodafone. So give it time.