I got a virtual phone number which helped with the application. When they tried to send me a text to add my card to ApplePay, it didn't come through. I don't know about Google voice but my impression is that if verification text messages don't get through, it will be difficult. I've also tried to get a Google Fi sim but it keeps accepting my order then rejecting it before shipping - even sending it to my US address.
I also have a Citi US CC and this one is registered to my Au address. Recently received a letter they will cancel it and my reward points in July. With the $A falling so much, apart from achieving a US CC, I don't think there's any advantage in earning reward points on the US card if that's the mean reason for having it.