Practical Benefits of SIP Trunking

Jun 28, 2022
Practical Benefits of SIP Trunking

Despite the fact that everyone nowadays carries a personal cellphone, business phones aren’t going away — but they are changing. Like many services, business telephony is moving to the cloud, thanks to technology like SIP trunking, which offers businesses advantages such as quick provisioning, low costs, and no equipment to procure or maintain.

It’s a big change from the way business telephony used to run. In the good old days before the internet was everywhere — say, 1990 — telephone calls ran over copper wires from customer premises to analog switches in carrier central offices. If you ran a business and wanted to give your employees individual phones, you installed equipment called a private branch exchange (PBX). The phone company would run a line from their network to a punchdown block in a wiring closet at your location, and your technical team would run internal wiring to employees’ cubicles and drop fancy phones on top of their desks. Together the phones and the PBX supported advanced features like call hold and call forwarding. At least they were advanced compared to what people could do with their home phones.

The World Wide Web was invented in 1993, and within a few years it was clear that the internet was going to be a global network that could connect everyone and everything — including phones. Voice and video traffic could cross the network by using networking protocols like Internet Protocol (IP). The advent of voice over IP (VoIP) led to the development of the IP PBX, a hardware box (either a purpose-built device or a general-purpose server running software such as Asterisk, the first open source IP PBX) that translated between circuit-switching telephone calls and packet-switching networks.

A SIP of VoIP protocols

In order for network devices to communicate with each other, they have to agree on common data and transmission formats, or protocols. Session Initiation Protocol (SIP) was developed in the late ‘90s to provide a common way for devices and applications to initiate, maintain, and terminate real-time multimedia sessions involving voice and video. SIP has become one of the most common VoIP protocols.

That explains “SIP”; what about “trunking”?

In the telephony world, a trunk line is that cable that brings service to a building. Thanks to VoIP and SIP, trunks can now be virtual, running over the same network as a company’s data. Today, telephony and networking are generally combined into what we now call unified communications.

SIP trunking benefits

SIP trunking gives businesses a host of benefits.


With SIP trunking, businesses can add numbers easily whenever they need them, and each number can make and receive unlimited local and long-distance calls.


You can add as many numbers as you need, and drop them when the need goes away. You pay only for what you use.


With a number from the public switched telephone network (PSTN), you can only make and receive calls from wherever your phone is. A SIP endpoint can move to almost any device, so employees can be reached when they’re in the office or working from a coffee shop.


Working with the phone company can make you want to tear your hair out. Managing SIP trunks is much easier and less time-consuming.

Cost savings

Pricing for SIP lines is attractive. With Plivo, businesses pay a minuscule monthly fee and less than a penny a minute (in the US; pricing varies by country) for outgoing voice calls, which is less than the cost of a call on a number leased from a phone company.

SIP trunking offers another cost advantage — no hardware phones necessary. Any network device with a microphone and speakers can act as a softphone. That saves companies the cost of procuring and maintaining telephones — though if you prefer to have a separate device for phone calls, you can buy SIP handsets.

Virtual local presence

You can use SIP phone numbers with any area code and exchange that your provider offers. That means you can seem to be local to your customers, who tend to like doing business with local companies, even if you’re based far away.

And SIP advantages go beyond that. You can create SIP endpoints that let you invoke custom functionality when you make or receive calls. Any Plivo application can implement the logic needed to control a registered SIP phone. Read our documentation to get a feel for how that works.


Ready to jump into SIP trunking with both feet? Just be aware of a couple of potential drawbacks.

With SIP trunking, if your network goes down, so does your phone system. You can use an old-school PRI (Primary Rate Interface) as a backup option, but weigh the costs and benefits. If your network is 99.9% stable during business hours, you might not want to pay for phone lines you never use. Also consider that when the network is down, you probably can’t get much work done even if you have access to your phones.

Another disadvantage is that SIP traffic is network traffic, and if your network is already congested, you may worsen your problems. However, bandwidth is cheap nowadays, so you can solve that problem by throwing money at it.

Plivo’s solution for SIP trunking

Once you’ve done your research, check out Zentrunk, Plivo’s SIP trunking service. It’s cloud-based, so there’s no need to acquire or manage any hardware on-prem. Zentrunk offers guaranteed call quality, high uptime, and unlimited concurrent calls. You can purchase and instantly provision SIP numbers for inbound calls in dozens of countries on every continent (except Antarctica), and make calls from your SIP numbers to virtually everywhere on Earth.

Give Zentrunk a spin. Dive into our Quickstart guide, sign up for a Plivo account, and start connecting with the world.

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