Using SIP Trunks with an Open Source PBX

SIP Trunks + Open Source PBXA recent study by The Eastern Management Group predicts that by 2018, 42% of all businesses will send their toll traffic on SIP trunks.  The reason for this is simple.  Businesses have discovered that SIP is an effective way to significantly reduce communications cost without sacrificing reliability or functionality.  Of course, using SIP trunks does not eliminate the need for call control or PBX functionality.  Fortunately for cost conscious buyers, there are a number of open source PBX solutions that can be used with SIP trunks to slash costs even further.  Here are a few of the most popular:


With more than one million Asterisk-based communications systems in use in over 170 countries, it is among the most popular PBX solutions of any type.  It is a free, open source framework for building communications applications and is frequently paired with SIP trunks.  It runs on an ordinary computer and can serve as the basis for a complete business phone system or it can be used to extend an existing PBX.  The Asterisk open source project is sponsored by Digium.

The Asterisk framework was built to be used by developers.  In order to build custom solutions using the platform, it is necessary to have a working knowledge of Linux, script programming, telephony and networking.  However, many businesses without these technical skills still leverage Asterisk by working with an integrator or consultant.  There is also an AsteriskExchange community marketplace which contains a list of available pre-built solutions.


For those who want the ease and simplicity of a graphical user interface, FreePBX is an open source GUI that controls and manages Asterisk.  It can be installed and configured alone, or as part of a distribution that includes the OS, Asterisk the GUI and other dependent software.  FreePBX is easy to customize and can run in the cloud or on-site.  It is used by very small home-based businesses and large multi-location enterprises alike.

As with Asterisk, commercial models are available, this time from the sponsor Schmooze Com Inc.  Paid support, integration and other services are also offered.  FreePBX can be configured to work with SIP trunks.


Another, free, open source option is FreeSWITCH.  It is a telephony platform that uses common communications protocols to support audio, voice, text and other media.  It serves as a platform on which many telephony applications can be developed using available free tools.  The solution’s support of a variety of audio codecs make it ideal for SIP trunks.  Its modular design simplifies the development effort required.  FreeSWITCH comes loaded with a set of modules to enable basic functionality and others can be added to meet additional requirements.

These are just a few of the available VoIP related open source projects out there.  Others include Elastix and PBX in a Flash.  If you elect to use an open source solution for your communications needs, it is important to ensure that your SIP trunk provider is compatible with these types of solutions.  (SIP.US supports all of the applications mentioned along with many others.)

SIP trunks and open source PBX solutions are an excellent way to reduce costs, increase flexibility and ensure a solution that is just right for your business.  However, this flexibility does add a degree of complexity and those without telephony and networking experience should consider working with a trusted partner to ensure a smooth implementation.

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