

Like Google Fi, it’s a VoIP (voice over internet protocol) service so coverage should be the same as Fi.
Strictly speaking Google Fi is a MVNO. After losing Sprint/US Cellular access a while back nowadays they are a T-Mobile reseller e.g. you’re getting access to T-Mobile’s network and coverage with Google Fi.
For what it’s worth my Google Voice phone number does show up as being classified as a VoIP number so that might be more along the lines of what you’re thinking. The phone number I have on Google Fi does not show up as VoIP.







Like some of the other comments, if you really need a DE then maybe give XFCE or LXQt a try. The distro itself won’t matter too much in your scenario.
I do have an old laptop that has run Debian/Ubuntu + Gnome fine, not at all fast but usable for my needs. Mines has 4 GB RAM, get the feeling that going under 4 GB may be a bit much.
Otherwise Linux is perfectly usable without a DE if you’re willing to stick to the terminal for all your usage.