We do not provide support for installing messages in your phone system, unless you subscribe to AMS, our enterprise-grade audio management system.
AMS is available customers that use:
RingCentral
AT&T Office@Hand
Avaya Cloud Office by Ring Central
BT Cloud Work
Telus
Rainbow Office
Unify Office by RingCentral
RingCentral with Verizon
...and more providers to come soon.