→ 3 x Satellites - 2 x Communication devices per person
→ 1 Antenna per settlement/ town
→ 1 Charging stations per housing
→ Device settings
Possible problems:
→ Satellite breakdown, power outages, phone malfunction
Possible solutions:
→ Spare Satellite, generating power manually, set up rules for use
The amount of people living on the planet would not matter. As the solution would work with any amount of cell phones.

Diagramm of Setup on Mars

Local Communication