Telephony is the technology of voice communication over distances. It includes the phones, the networks, and the protocols. It began with the telegraph and the telephone. It evolved through circuit switching, digital switching, and VoIP. It is the foundation of voice communication.

Traditional telephony used analog signals over copper wires. The public switched telephone network connected calls with circuit switches. Digital telephony converted voice to bits. VoIP sends voice over the internet. Each generation improved quality and reduced cost. The voice is now just another data stream.

Telephony technologies

• PSTN: traditional circuit-switched
• ISDN: digital over phone lines
• VoIP: voice over IP
• Mobile: cellular voice
• Unified communications: voice, video, messaging

Telephony is not just phone calls. It includes voicemail, conferencing, and call centers. It is embedded in business systems. It is regulated for emergency services and universal access. The telephone is a device. Telephony is the system. It connects the world's voices.