Extremely ignorant Q re how groups manage phone bills

It just depends on the carrier. Generally, with 4 people on a group plan, everyone gets half off what it’d cost a single person.

e.g. for 1/2/3/4 people, per person/month, assuming the most basic unlimited plan:

Carrier 1 Line 2 Lines 3 Lines 4 Lines
Google Fi (MVNO) $50 $40 $30 $25
T-Mobile $50 $45 $30 $25
Verizon $65 $55 $40 $30
US Cellular $60 $58 $40 $30
AT&T $66 $61 $46 $36

A MNVO is a cell phone company that doesn’t own and operate their own towers, but instead leases extra capacity from other providers and resells it under their own brand name and pricing and provides their own customer service.