DNS tunnelling is just another tunnelling technique. Usually, it is called VPN over DNS too, it is just naming. What it makes it very popular is that not all carriers or network administrators are aware of it or if they are, they don't know exactly how to stop it. Rogers, one of the biggest telecommunication carrier in Canada and Telcel the biggest player of mobile telephony in Mexico, both allow DNS tunnelling (I don't doubt others carriers do as well), so when you run out of data in your plan you can still connect if you configure it in your mobile. This is because smartphones need to connect to some carrier servers regardless if you have the right to 2G/3G/4G data access or not; smartphones still have access to the local DNS server. Local networks have the same symptom because DNS is used to access many IT services like the Active Directory, it is very difficult to differentiate between a true legitimate DNS query and DNS tunnelling traffic without the proper tools.
Because of this, I am going to describe how this technique works.
Voxout it is the trunk service that Voxbone offers to make outgoing calls and emergency ones. I must say it is tricky to configure it, the PDF they give as a tech guide is next to useless and so far, if you google, you won't find any example of FreeSWITCH gateway configuration with Voxout. I will talk about how I did it.
Yesterday, I have published in the OKay's RPM repository the RPMs for the Enhanced CDR Importer (ECI) for FusionPBX 1.1.1. The ECI is a drop-in replacement for the CDR importer that comes with FusionPBX. It has a plugin architecture allows you to easily export the CDR into third-party software such as Billing for FusionPBX, Helpdesk, CRM or Bigdata applications.
RPM's are available for Centos 6 and 7. And you can find it if you type yum search fusionpbx-enhanced-cdr-importer.
The ECI requires FusionPBX 4.4 or better. Release 1.1.1 fixes some FusionPBX 4.4 incompatibilities.