For U.S. users without working VoLTE, you could try this as an interim solution:
-
Get a jmp.chat account for $2.99/month (current Beta pricing). It includes calling, texting, and picture messaging. Port from your mobile carrier to jmp.chat, and add the account to your SIP dialer (or use Linphone dialer, etc.).
-
Get a data-only international SIM. I just saw, as one example, that Vegolink’s new U.S. pricing is $7/gigabyte for roaming on AT&T and $15/gigabyte for T-mobile. Data roaming in many other countries is cheap as well.
So, for $2.99 a month (EDIT: and some potential additional cheap costs for outgoing minutes), plus $7 for each gigabyte (non-expiring as long as you top up before one year has elapsed), you could completely replace your normal carrier and not be subject to VoLTE restrictions. One (major) downside is that you wouldn’t have e911 support from jmp.chat.
I don’t have any experience with Vegolink or info about their reliability and business practices, so I’m not specifically recommending them, only bringing them to your attention. Nor do I know anything about the owners, other than what is listed for company info: https://opencorporates.com/companies/cy/HE342741. You’ll have to do some research and decide if you want to do business with them.
I don’t have any experience with jmp.chat, either. I have used my VOIP account with Android’s SIP dialer, and it works well.
I do have experience with a similar international SIM company, Surfroam. I was not happy with their business practices.