Extensions are at the core of every PBX. Extensions on a PBX have multiple numbers, DIDs and ANIs for inbound and outbound call identification. Each extension has a name, a company position and passwords for web and SIP access. Each extension may have its own timezone, web and IVR language and have an image associated with the extension which can be shown on VoIP phones that support showing a photo caller-ID. Extensions can have their own ringtone, permissions for various actions, address book and music on hold source.


The PBX handles basic redirection features like do not disturb (DND) and call forward on busy, on timeout, when there is no registration or of all calls. When calling a specific PBX, other extensions can also be included in the call like in a hunt group for every extension. Each extension may have multiple registrations which ring simultaneously when the PBX wants to engage with the user.


Every extension can have multiple cell phones associated with it. When someone calls the extension, the PBX will immediately or after some time include the cell phone as if it was a registered extension. This feature can be limited to specific times during the day so that users don’t get annoyed by the calls after hours. Cell phones can also be used to place outbound calls. This makes sure that the extension outbound number is shown on the caller’s display and calls are charged to the PBX, which can be important for international calls. Cell phones can also be part of hunt and agent groups, further extending the user’s mobility even in environments like call centres or sales and support groups. The PBX can send text messages to the user’s phone, for example when a new voicemail message is available. Those messages can even include the audio recording if supported by the text provider.


Calls to and from extensions can be recorded automatically or manually. They can be recorded if the call was within a hunt group, an agent group or a direct call to the extension. Outbound calls can be recorded as well. Depending on the VoIP phone being used, the recording status can be made visible on a button of the phone, where the recording can also be turned off. The recordings can be written to the local file system or using the SIPREC standard. When they are written to the file system, users can play them back through the web interface or through a special code that starts the playing back of all call recordings. This is useful when users or managers have time to review call recordings. Recording of emergency calls can serve as valuable proof in case of prank calls, especially in public environments where people have access to phones without further authentication.


Transferring calls is a core feature of every PBX. The PBX supports various attended and unattended transfers that are triggered by the user’s VoIP phones. In addition to that, calls can be parked on park orbits. In order to avoid caller starvation, the PBX can automatically reassign parked calls or transfer them out of the orbit. Special modes are available to transfer calls to and from cell phones, so when arriving or leaving the office, the call does not have to get disconnected.


Receiving unwanted and sometimes threatening and dangerous calls has become a problem for many businesses that costs valuable time. The PBX integrates with several SPAM score providers that determine if a number is considered SPAM and returns a score. Depending on the score, the PBX decides what to do with the call. The internal address book can also be used as a source for SPAM scoring, including the possibility to allow calls only from whitelisted numbers. This includes handling of anonymous calls.