It is possible, with a workaround, to play a tone on the PA1 before making an announcement.
The only way to do it is to set as custom ringtone the tone you want to play, and to delay the auto answer for a couple of seconds: this way the PA1 will play the ringtone before answering the call automatically, and the tone will be heard before the announcement.
This can be done following the steps below, and it requires an Alert-Info SIP header from the PBX to work.
You need to set the parameter "vip_ring_sound" to “custom”.
You need to set an URL on the parameter "custom_melody_url".
The Auto Answer on the PA1 needs to be disabled (user_auto_connect), but the answer_after_policy parameter needs to be set to "always".
You then need to use the Alert-Info SIP header from the PBX to allow the PA1 to automatically answer the call with the required delay, it needs to send something like this:
This way the PA1 will auto answer only if there is an Alert-Info SIP header: in this case the header value sets the delay in the auto answer at 2 seconds so the phone rings for 2 seconds, playing the tone you are using as a custom ringtone, and then answers the call.
You can also avoid the auto answer tone from the PA1, if you don’t like it, and you would need to change the parameter "auto_connect_indication_tone".
Now when calling the PA1, if the PBX is sending the correct Alert-Info header, the device will ring for the specified amount of seconds before answering the call automatically: this will allow you to play the required tone before being able to speak on the calling phone side, and to make an announcement.