I use H2o wireless phone company they will switch to volte for Costomers I may going to be ok

It depends on the carrier. I have H2O wireless and a factory unlocked iPhone 7. H2O Wireless was sending me text messages that said I had to upgrade, but Apple (an ATT MVNO) & ATT say it's compatible.

I chatted with H2OWireless's phone support and they said:

H2OWIRELESS  Isis-h2o:

You can confirm in Settings> Mobile networks> Network type: You need to check if you have 4G or LTE available, if you have it you do not need to worry

My phone doesn't have those options, or what's listed on https://support.apple.com/en-us/HT203124 (It only has Settings/Cellular/Cellular Data Options) so I told H2O that, and that it says "LTE" up in the status bar: ".iI| H2O LTE" and H2O said:

 H2OWIRELESS  Isis-h2o:

If your device is LTE it will work fine, you can ignore the message.

For my iPhone 7 with iOS 15.2, and the different menus, it makes it hard to follow the instructions on advice like https://support.apple.com/en-us/HT203124

My Settings/Cellular/Cellular Data Options does not match the Apple advice on https://support.apple.com/en-us/HT203124 but the little "LTE" in the title bar might be enough for the H2O chat person to say it will work fine:

H2OWIRELESS  Isis-h2o:

If your device is LTE it will work fine, you can ignore the message.

(Recent models of) iPhone support VoLTE. About the LTE options on your iPhone - Apple Support