I need to receive/make calls & texting, very infrequent .
a) Aust (2nd) a virtual mobile number to forward to my mobile for privacy.
b) USA virtual mobile phone number to forward to my mobile
Willing to pay for number but I don't want ongoing costs.
Have a look at Talkatone for the US. I use it to receive my 2FA codes
With voWIFI, you can call and text overseas using your Australian Number; as long as a WIFI internet connection is available.
(Internet over cellular is not supported, unless you want to pay for roaming)
For Australia, Crazytel ($8 per month). You can use the app on your mobile phone so you don't need to pay for call forwarding. They don't offer US numbers however.
Currently I pay $10/m with amaysim with unlimited calls & 10Gb
It might be hard to find with no ongoing costs. Generally companies like to make a profit.
Doesn't sound suss at all.