Insights & Resources6 min read

Inbound SIP Trunks vs Outbound | Business Guide

Go in-depth with inbound and outbound SIP trunking, and understand which features make the most sense for your business needs.

Brian Segal
Inbound SIP Trunk phone screen
There are a lot of ways to classify calls. And there are reasons for classifying calls according to their type. But classifying calls by which direction they travel is one of the most useful ways to categorize your calls.
That’s why understanding inbound SIP trunks vs outbound is valuable, and that’s what this article will help you do.

Inbound vs Outbound SIP Trunking

In short, there are two major categories of calls: inbound and outbound. When someone calls your personal or business phone number, that’s an inbound call. If the call goes the other direction—you call someone else—that’s an outbound call. Typically, your inbound and outbound calls connect through the same SIP trunk.
However, it’s possible to have one SIP trunk for your inbound calls and another SIP trunk for your outbound calls. Or you can have a SIP trunk for calls that go in one direction, and a PRI trunk for calls that go in the other direction.
This may sound odd. But there are reasons to have separate trunks (either a SIP trunk or PRI trunk) for your inbound and outbound calls.

What is Inbound SIP Trunking?

Inbound SIP trunking is using a separate SIP trunk for inbound calls, while using a separate SIP trunk or PRI trunk for your outbound calls. This enables you to pay for only the inbound calling features you need, while keeping your outbound calling more affordable.
Inbound and outbound calls have different capabilities, and therefore different feature sets (which are covered in the next section). If your business only needs the features of inbound calling, you can get a fully featured inbound SIP trunk for your inbound calls. Then you can pair this with a relatively stripped down outbound trunk to avoid paying for outbound call features that you don’t use.
Whether or not this is a good option for your business will depend on how you use your telephone infrastructure.

Inbound SIP Features

Most inbound SIP features are designed to improve the caller experience. Inbound SIP features are designed to save customers from busy signals or reaching the wrong person or department, and make it as easy as possible to call you.
These are the features you can add to your inbound SIP trunk:
  • Toll-free phone numbers: Toll-free phone numbers make it free for customers to call you. Obviously, this is ideal for sales and customer service lines, where making the customer pay for the call is bad practice.
  • Custom phone numbers: Custom phone numbers—especially numbers that spell out a word based on the letters on the keypad—make it easy for customers to remember your business phone number. Custom phone numbers are also great if you need to use a non-fixed VoIP number to make it look like your phone number is local to the caller’s geographic area.
  • Direct voicemail delivery: If you’d rather not put customers on hold when all your customer service representatives are busy, voicemail is your best option. And, if your business model requires customers to call certain employees directly, direct voicemail delivery is mandatory. This will deliver voicemail messages directly to your employees’ inboxes, rather than a central business inbox.
  • Voicemail transcription: No matter how you need your voicemail messages delivered, voicemail transcription can make it much easier to retrieve and review. With voicemail transcription, voicemails can be automatically transcribed and delivered via chat or text message. That way your employees can get their voicemail messages without having to call their voicemail box.
  • Custom call routing: In an office or organization with many phones and phone numbers, custom call routing is vital for connecting customers to the right people. Custom call routing also makes it easy to reconfigure your call routing when people move to different offices, get new phone numbers, or replace their phone.
  • Call recording: There are multiple reasons to record calls. The most common reason is training. But, in some industries, call recording may be required for legal compliance.
If your business requires any or all of these features, an inbound SIP trunk is the best solution. PRI trunks simply aren’t capable of delivering all of these features.
Next, an outbound SIP trunk offers a different feature set.

What is Outbound SIP Trunking?

Outbound SIP trunking is the opposite of inbound SIP trunking: placing your outbound calls on a separate SIP trunk from your inbound calls. Your outbound SIP trunk enables your business to reach out to customers from multiple phone numbers and integrate your outbound call infrastructure with your data management software.
Using a separate outbound SIP trunk is ideal for businesses that make a lot of calls, while fielding fewer inbound calls. Think telemarketing call centers or census outreach contractors.
An outbound SIP trunk gives you all the outbound phone numbers and features you need, while maintaining just enough ability to accept calls. But, just like inbound SIP trunking, whether or not you should use a separate inbound SIP trunk depends on your ratio of inbound to outbound calls, and what capabilities you need for making calls.

Outbound SIP Features

The main idea of outbound SIP features is making it easier for you to call the right phone numbers and manage all the data associated with your phone numbers.
An outbound SIP trunk can deliver these features:
  • CRM and data management software integration: If you make high volumes of outbound calls, you most likely have a lot of data attached to the phone numbers you call. In these cases, most businesses use a CRM system or other data management solution. And it’s best if your phone number data is integrated into your calling infrastructure, so employees can access the information on-demand, when they make calls.
  • Call data capture: Detailed call records are valuable for analyzing your outbound calling and optimizing call flows, maximizing completed calls, and evaluating employee performance. However, capturing and maintaining call data may also be required for regulatory compliance, depending on your industry.
  • Caller ID: Caller ID is essential for any business that makes calls. If people don’t know who’s calling them, they will usually ignore the call. But it’s also important that your business is correctly identified, regardless of which device or phone number you’re calling from, especially if you have many phones and phone numbers that need to be identified as your business numbers on the caller ID screen.
  • Emergency calling: Making emergency calls through a SIP connection isn’t quite the same as making an emergency call on a traditional telephone network. But a quality outbound SIP trunk provider will be able to connect emergency calls on your outbound SIP trunk. So you can use your outbound SIP trunk for everything, including your emergency call services.
Typically, these features are most useful for businesses that have a very high ratio of outbound to inbound calls and multiple outbound calling phone numbers. But, even if you receive more calls than you make, these features will make things easier when it’s time to make calls.

Get Started with Telnyx

If you recall from the beginning of the article, it’s possible to have your inbound SIP trunking and outbound SIP trunking on the same trunk. And this is usually the most cost efficient and reliable solution.
Even if you only use SIP trunking for calls in one direction, with a PRI trunk for calls in the other direction while you make the transition from traditional phone lines to SIP trunking, you’ll get the best pricing and reliability if all your SIP trunking comes from the same provider.
That’s where Telnyx comes in. Telnyx offers both outbound and inbound SIP trunks. And the Telnyx network is capable of supporting all the features you need, regardless of your calling requirements. Talk to a Telnyx expert to find out how you can get everything you need from a single SIP trunking provider.
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