I have made two trips overseas recently and on both occasions was unable to use Virgin Mobile phone services. Phone is Samsung Galaxy A20 s running Android 11.
In USA got this message: "Welcome you are roaming on AT &T. Due to network technology compatibility traditional voice calls will not work. Please use data, SMS and app- based calling."
Notified Virgin but no resolution so no phone calls possible.
Now for Switzerland. Texted virgin and got an access code as instructed for phone, internet and picture messaging. Entered details but no proper phone connection. On trying to call a UK number there would be a ping and then nothing. The call was logged as 2 seconds. Same again 6 or seven times. However suddenly a good connection. Next 6 days was able to make 3 successful calls from more than 30 trials. Nothing to do with signal coverage as also tried at Zurich airport. Unable to call or text virgin due to the lack of connection.
This is just a warning for others. Don't offer advice about how to fix the problem because its Good bye Virgin as I am now going out to join another phone services provider.