long time we requesting adding (scheduler) to (Announcement Center) this is very important option for schools and hospitals … etc , with this small add and SIP speakers (or GXV3500 connected to amplifier ) we can easily setup IP public Address system, some of your competitors like zycoo they have this options in there PBX 4 years ago, they now also have special server for it, with collection of SIP speakers. its really so important option
Request was added via ticket system ?
You can use scheduler caller for this (external app)
For android example (juts add gs wave or another sip caller and invoke dialling:
I do not test it, but that should do trick you lack in current soft.