PSTN $($Public Switched Telephone Network$)$ and coaxial cables are utilized by ISP providers like EE$,$ BT$,$ TalkTalk, Virgin Media, and Sky due to their established infrastructure and specific performance advantages.

PSTN:

Established Infrastructure: PSTN has a vast, well$-$established network that spans globally, making it accessible and reliable. Providers like BT and TalkTalk leverage this infrastructure to deliver consistent and dependable voice services.

Reliability and Quality: PSTN offers high reliability and call quality due to its dedicated circuit$-$switched nature, ensuring minimal call drops and clear voice communication.

Emergency Services: PSTN supports emergency services $($e$.$g$.,911$ or $112)$ with precise location tracking, which is critical for safety and compliance with regulations.

Power Supply Independence: PSTN lines typically continue to function during power outages, providing an essential service in emergencies.

Coaxial Cables:

High Bandwidth: Coaxial cables, used by providers like Virgin Media and Sky$,$ support higher bandwidth than traditional PSTN$,$ making them suitable for high$-$speed internet and digital TV services.

Robust Data Transmission: Coaxial cables offer greater resistance to electromagnetic interference, ensuring stable data transmission over long distances.

Converged Services: Coaxial infrastructure allows the delivery of multiple services $($internet$,$ TV$,$ and phone$)$ over a single line, providing convenience and cost efficiency for both providers and consumers.

Upgradability: Coaxial networks can be more easily upgraded to support newer technologies $($e$.$g$.,$ DOCSIS standards$)$ for faster internet speeds without extensive infrastructure overhaul.

In summary, PSTN is used for its reliability and established infrastructure, particularly for voice services, while coaxial cables are chosen for their high bandwidth capabilities and suitability for converged digital services. This combination allows ISP providers to meet diverse consumer needs effectively.