Calls go through the gateway will get the music on hold using this method if you select PSTN gateways to provide to provide MOH.
If you change the Call Progress tone, a gateway reboot is needed.
If you change the prerecordedtones.dat, please check the size for prerecordedtones.dat is allowed.
For the details, see the section “Q. Is There Any Way to Provide Music on Hold to Your PSTN Callers (If Using Lync Phone Edition or other device that doesn’t provide endpoint MOH)” at
http://windowspbx.blogspot.in/2011/07/questions-about-microsoft-lync-server.html
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