Tlhokaina A high-res audio player that is capable of making phone calls over the data network. Something like the FiiO M27 This device can already make VOIP calls over wifi - I wouldn't think it would be too difficult to add cellular capability.
Tandara GOS has no say in what will be included, the manufacturer decides that. Manufacturer will be announced in a month, so you can look what the phone will look like from their previous releases (current, likely guess is Motorola)
Vincent96 Phone calls over the internet? Like Signal? Or VoLTE? These already exist. If you want high-res audio you can already plug in a USB C DAC.