Unlike Panasonic PBX systems, this isn’t actually a feature of SIP. You can send a stream of music to device, but it’s a call and makes the device “busy” and therefore it becomes a really expensive MP3 player.
Nope - unless you have more than one extension on a phone, it will only take one call at a time. Even then, if the phone is busy, it will always prefer the existing SIP connection. To accomplish this, you’d have to use an AMI script that sends a “hang up” to the phone to terminate the “noise” call so you can page to it. Even then, setting this up will require considerable AMI programming to log into the data stream, identify it, terminate the call, then play another file back.
Paging Pro has this feature, but the phones have to be configured to automatically play the recording if you are using it in a “paging” context.
If all you want is to send a file, you can do that using a Call File. The setup for call files is relatively straightforward, but there’s nothing in FreePBX that will allow you to manage the source file for your call. Note that some of this (scheduling the call, for example) is part of Paging Pro. You may even be able to set up the “playback” file from there, but there’s more flies in that ointment.
As with all automated calls, the “answer” signal causes the file to start, so steps may be required to get the audio processed correctly. For example, any extension that can receive FAXes will automatically answer the call (to listen to it) and will then ring if the call isn’t to a FAX. Some Cell carriers, as well, preemptively answer their calls before they are presented to the recipient, cutting off the start of the call.