Choosing the right line type for voice

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<p id="docs-hc-snippet" style="display: none;">There are three types of phone lines:</p>
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<p id="docs-ai-summary-content">Choose the right voice line type based on your support needs: PSTN for simple, reliable calling, digital lines for VoIP with no published phone number and usage-based cost, and SIP-IN for call forwarding, BYOC, AI agent escalation, and partner app integrations. The article helps you compare features and pick the best line for voice support.</p>
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<p class="p">There are three types of phone lines: </p>
<ul class="ul" id="Talk_choosing_line_type__ul_mtb_pns_12c">
<li class="li">Standard lines using Public Switched Telephone Network (PSTN)</li>
<li class="li">Digital lines using Voice over Internet Protocol (VoIP)</li>
<li class="li">SIP-IN (Session Initiation Protocol) lines using Internet Protocol (IP)
technology</li>
</ul>
<p class="p">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.</p>
<p class="p">This article contains the following topics:</p>
<ul class="ul" id="Talk_choosing_line_type__ul_kmz_4js_12c">
<li class="li"><a class="xref" href="#topic_rlv_rks_12c">Understanding standard PSTN lines</a></li>
<li class="li"><a class="xref" href="#topic_zmm_sjs_12c">Understanding digital lines</a></li>
<li class="li"><a class="xref" href="#topic_bcd_tjs_12c">Understanding SIP-IN lines</a></li>
</ul>
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<div aria-labelledby="ariaid-title2" class="topic nested1" id="topic_rlv_rks_12c">
<h2 class="title topictitle2" id="ariaid-title2">Understanding standard PSTN lines</h2>
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<p class="p">Standard PSTN lines (commonly referred to as standard phone lines) are the
backbone of traditional telephony, connecting calls through the Public Switched
Telephone Network. </p>
<p class="p">PSTN lines offer the following advantages:</p>
<ul class="ul" id="topic_rlv_rks_12c__ul_rkj_wks_12c">
<li class="li">Known for their stability and reliability, making them a trusted
choice when you want to prioritize uninterrupted communication.</li>
<li class="li">Easy to set up and use. There’s no need for specialized equipment or
extensive training.</li>
<li class="li">Accessible to all customers, regardless of their technological
capabilities, ensuring that you can reach a broad audience.</li>
</ul>
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<div aria-labelledby="ariaid-title3" class="topic nested2" id="topic_jy2_sks_12c">
<h3 class="title topictitle3" id="ariaid-title3">When to use a standard PSTN phone line</h3>
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<p class="p">Use a PSTN line when you need straightforward, reliable communication
without the need for advanced features.</p>
<p class="p">To get started, see <a class="xref" href="https://support.zendesk.com/hc/en-us/articles/4408824192026" target="_blank">Adding phone lines</a>.</p>
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<div aria-labelledby="ariaid-title4" class="topic nested1" id="topic_zmm_sjs_12c">
<h2 class="title topictitle2" id="ariaid-title4">Understanding digital lines</h2>
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<p class="p">Digital lines use Voice over Internet Protocol (VoIP) technology to offer
an upgrade from traditional PSTN lines. </p>
<div class="note note">
<span class="notetitle">Note:</span> When you turn on messaging for your account, Zendesk automatically creates a
digital line for each brand. These lines are named <em class="ph i">&lt;Brand&gt; digital
line</em>, even if you haven't created a digital line yourself.</div>
<p class="p">Digital lines offer the following advantages:</p>
<ul class="ul" id="topic_zmm_sjs_12c__ul_sfq_nks_12c">
<li class="li">No need to publish a phone number for your customers to call.</li>
<li class="li">Expand your voice support footprint across countries without the need
for phone numbers there.</li>
<li class="li">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 <a class="xref" href="https://support.zendesk.com/hc/en-us/articles/4408846483482" target="_blank">Number availability and pricing</a>.</li>
<li class="li">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.</li>
</ul>
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<div aria-labelledby="ariaid-title5" class="topic nested2" id="topic_yxw_sjs_12c">
<h3 class="title topictitle3" id="ariaid-title5">When to use a digital line</h3>
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<p class="p">Use a digital line when you want to combine reliability with advanced
features to improve your customer interactions.</p>
<p class="p">To get started, see <a class="xref" href="https://support.zendesk.com/hc/en-us/articles/1260805715389" target="_blank">Adding a
digital line</a>.</p>
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<div aria-labelledby="ariaid-title6" class="topic nested1" id="topic_bcd_tjs_12c">
<h2 class="title topictitle2" id="ariaid-title6">Understanding SIP-IN lines</h2>
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<p class="p">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.</p>
<p class="p">SIP-IN lines offer the following advantages:</p>
<ul class="ul" id="topic_bcd_tjs_12c__ul_z1x_1ks_12c">
<li class="li">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).</li>
<li class="li">Forward calls into Zendesk via SIP-IN without paying PSTN rates for
call forwarding.</li>
<li class="li">Connect with partner apps during the call flow, such as an external
IVR, to enable a more complex and integrated service experience.</li>
</ul>
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<div aria-labelledby="ariaid-title7" class="topic nested2" id="topic_qvt_tjs_12c">
<h3 class="title topictitle3" id="ariaid-title7">When to use a SIP-IN line</h3>
<div class="body">
<p class="p">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.</p>
<p class="p">To get started, see <a class="xref" href="https://support.zendesk.com/hc/en-us/articles/8397091234586" target="_blank">Adding a SIP-IN line</a>.</p>
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