VoIP
VoIP, or Voice over Internet Protocol, is a method for carrying voice calls as digital data over internet protocol networks rather than relying entirely on dedicated circuit-switched telephone paths. It can connect software applications, business phone systems, carriers, and the public telephone network.
How VoIP works
A VoIP call separates several jobs. Signaling establishes, changes, and ends the session; SIP is a common protocol for that role. The spoken audio is encoded by a codec, divided into packets, and transported as a media stream, commonly using RTP. A provider or gateway can connect the IP side of the call to a conventional phone number on the PSTN.
Because packets travel across networks independently, call quality depends on more than raw bandwidth. Delay, jitter, packet loss, codec compatibility, and network configuration can affect what each party hears. Security and identity also span several layers, including access controls for call setup and protection for signaling or media where the deployment supports it.
VoIP is broader than an internet calling app. A business may use it behind a PBX, through a SIP trunk, inside a contact center, or as the connection between an AI phone agent and a telephony provider. A caller can still dial an ordinary phone number even when much of the call travels over IP.
Why it matters for AI phone calls
VoIP gives software-based agents a practical path to receive and place calls without behaving like a physical desk phone. It also introduces integration choices: who supplies the number, where calls are routed, which codecs are accepted, how caller identity is presented, and what happens when the destination is unavailable. These choices affect reliability and troubleshooting.
When evaluating a voice agent, buyers should distinguish the agent's conversation engine from its telephony connection. A good test covers inbound and outbound routing, audio in both directions, transfers, failure handling, and the network conditions expected in production.
In practice on ThunderPhone
ThunderPhone provides inbound demo U.S. numbers for testing. Production numbers can be brought through supported direct VoIP connections or manual SIP configuration for any SIP trunk. Verified imported numbers support inbound and outbound calling; demo numbers are inbound-only and are not intended for production.