Go to Voip providers and select the relevant provider
On edit voip provider go to the "advanced" tab
Untick "PBX delivers Audio" and tick "Supports Re-Invite"
If the provider supports it this should give your callers their on hold music. You should also check that transfers are working OK after making the changes as a provider that does not fully support Re-Invites set this way may cut off calls on transfers, call parks etc.
You will also need to ensure that all extensions are also set this way (Untick "PBX delivers Audio" and tick "Supports Re-Invite") or they will get your music.
I'm afraid this didn't work.. I just get the 3CX music. I've restarted all 3CX services, and checked that the extension I was using had the same options.
I don't have a 3CX system available but my colleague who has access to a Version 10 (SP6 I think) tested it for me.
It would only work with their music if G711U and G711a were disabled
It worked on G729a and ILBC on some occasions however some of the time it would play silence. In addition if the call was placed on hold for a second time 3CX MOH was played.
Also it was not always possible to pick the call back up after it was on hold. In general he said it caused considerable reliability problems and he would not recommend trying it. Additionally he said their music on hold was bloody awful, but I guess that is only his personal opinion !!!