open-300x204A  study by The Eastern Management Group found that by 2018, 42% of all businesses will send their toll traffic on SIP trunks.  Why? Because people have figured out that SIP is an effective way to significantly lower communications cost while still getting reliable, flexible service.  SIP trunks provide connectivity to the PSTN (Public Switched Telephone Network), but you still need a solution for call management and unified communications features. Luckily for those concerned about minimizing costs, there are a several, very low-cost, or even free, open source PBX solutions that can be used in conjunction with SIP trunks to cut costs even further.  Here are a few of the most common:


There are more than one million Asterisk-based communications platforms in use in over 170 countries across the globe, making it among the most popular PBX solutions of any kind.  Asterisk is a free, open source framework for building communications applications. It is often paired with SIP trunks.  It runs on an ordinary PC and serves as the basis for a complete business phone system. It can be used to bring more unified communications features to another PBX system.  The Asterisk open source project is sponsored by Digium.

The Asterisk platform was built to be used by developers.  If you want to use it to build a custom solution, you need to have a working knowledge of Linux, script programming, telephony, and networking.  But don’t let that scare you. Many companies without these technical skills are able to benefit from Asterisk by working with an integrator or consultant.  In addition, the AsteriskExchange is a community marketplace which contains a list of available pre-built solutions.


FreePBX is an open source graphical user interface 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 configure and can run in the cloud or on-site.  FreePBX is popular with small businesses as well as multi-location corporations.

As with Asterisk, commercial packages are available and inexpensive. FreePBX is brought to you from the sponsor, Schmooze Com Inc.  Premium support, integration, and other services are also available.  FreePBX works well with most SIP trunking services.


FreeSWITCH is another great solution.  It is a unified communications software infrastructure that uses common communications protocols to support audio, voice, text and other media.  It allows for the development of many telephony solutions using other free software.  Because FreeSWITCH supports of a number of audio codecs, it ideal for SIP trunks.  It has been designed to make it easy to configure and customize. The software comes complete with a set of modules to enable basic functionality. Additional plug-ins can be added to meet more complex requirements.

These are just a few of the open source options in the market.  Others that we love include Elastix and PBX in a Flash.  If go the open source route for your business communications needs, make sure that your SIP trunk provider can support these types of solutions.  (SIP.US is compatible with all of the applications mentioned and many more.)

Pairing an open source PBX with SIP trunks is an excellent way to slash costs, get more flexibility and ensure a solution that is just right for your business.  But do use caution, this flexibility adds a certain amount of complexity. If you don’t have telephony and networking experience, you should consider enlisting a trusted partner to ensure a successful implementation.

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