Well they do NOT use mobile phone netwoks!
Heres bit of interting reading albeit a bit dated now but its the teams take, Reb Bull in this instance, but these days a version of TETRA is used. Trans Europen Trunked Terrestrial Radio, near as dammit is used..
External Link/Members Onlyand.. these days..
Formula 1 team radio communications primarily utilize a sophisticated
TETRA digital radio system provided by Riedel Communications. This allows drivers to speak to their race engineers and teams to coordinate strategy, monitor car performance, and ensure safety.
System and Technology
Provider: The main system is provided by Riedel Communications.
Technology: It uses a TETRA (Terrestrial Trunked Radio) digital trunked radio system, which provides numerous simultaneous voice channels.
Coverage: A network of antennas and receivers is placed around the entire track (roughly every 200 meters) to ensure seamless communication with the moving cars.
Hardware: Teams often use specific radios like the Motorola MPX600 portable radios and Riedel MAX headsets.
Privacy: While the audio from the car on track is shared with the FIA and some is broadcast for fans, communication in the garage is private. Also, drivers cannot talk directly to each other; messages to a teammate must go through an engineer first.
Communication Content and Rules
Communication between the driver and the pit wall is a critical part of race strategy and car management. However, the FIA (Fédération Internationale de l'Automobile), the sport's governing body, has strict rules about what can and cannot be communicated during a race to ensure the driver is "driving the car alone and unaided".
Permitted Messages
Safety information: Warnings about yellow flags, debris on track, or dangerous situations.
Pit stop instructions: When to pit and which tires to prepare.
Traffic updates: Information on where other cars are during qualifying or a race.
Irreversible problem alerts: Indication of a car problem that requires an immediate, irreversible action like pitting to fix it or retiring the car.
Team orders: Instructions relating to teammates' positions on track.
Prohibited Messages
Any messages related to the performance of the car or the driver, such as specific driving lines, braking points, or gear choices that help improve the driver's speed.
Fan Experience
F1 heavily features team radio snippets in its broadcasts and online content to provide drama and insight into the sport's tactics. Fans can listen to live, additional radio feeds via official F1 services like F1TV or through other platforms like Box Box Radio