Choosing the right line type for voice

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There are three types of phone lines:

Standard lines using Public Switched Telephone Network (PSTN)

Digital lines using Voice over Internet Protocol (VoIP)

SIP-IN (Session Initiation Protocol) lines using Internet Protocol (IP) technology

Each line type caters to different operational needs and communication strategies. This article describes the three line types to help you decide which one is right for you.

This article contains the following topics:

Understanding standard PSTN lines

Understanding digital lines

Understanding SIP-IN lines

Understanding standard PSTN lines

Standard PSTN lines (commonly referred to as standard phone lines) are the backbone of traditional telephony, connecting calls through the Public Switched Telephone Network.

PSTN lines offer the following advantages:

Known for their stability and reliability, making them a trusted choice when you want to prioritize uninterrupted communication.

Easy to set up and use. There’s no need for specialized equipment or extensive training.

Accessible to all customers, regardless of their technological capabilities, ensuring that you can reach a broad audience.

When to use a standard PSTN phone line

Use a PSTN line when you need straightforward, reliable communication without the need for advanced features.

To get started, see Adding phone lines.

Understanding digital lines

Digital lines use Voice over Internet Protocol (VoIP) technology to offer an upgrade from traditional PSTN lines.

Digital lines offer the following advantages:

No need to publish a phone number for your customers to call.

Expand your voice support footprint across countries without the need for phone numbers there.

No monthly charge for a digital line. You are charged only when you use it. To find out more about the cost of phone lines, see Number availability and pricing.

Control over the integration and who can call you. For example, you might choose to add a call button only for signed-in customers, or your VIP customers.

When to use a digital line

Use a digital line when you want to combine reliability with advanced features to improve your customer interactions.

To get started, see Adding a digital line.

Understanding SIP-IN lines

SIP-IN (or Session Initiation Protocol) lines use Internet Protocol (IP) technology to facilitate voice communication. SIP-IN lines are a modern, scalable solution that can adapt to evolving communication needs.

SIP-IN lines offer the following advantages:

Escalate calls from an AI agent. Connect a third-party AI agent to escalate calls to human agents when they cannot resolve their query. Use local carriers and forward calls to Zendesk via SIP to operate your business in that country with Bring Your Own Carrier (BYOC).

Forward calls into Zendesk via SIP-IN without paying PSTN rates for call forwarding.

Connect with partner apps during the call flow, such as an external IVR, to enable a more complex and integrated service experience.

When to use a SIP-IN line

Use a SIP-IN line when you want to connect third-party applications such as AI agents, or if you want to bring your own carrier.

To get started, see Adding a SIP-IN line.