The inevitable transition from older Key and PBX systems to IP-based phone systems continues, and Easy On Hold is at the forefront of IP music on hold. With its newest release, IP-PBX systems provider IPitomy allows integration of the Easy On Hold streaming solution for music and messages on hold.
The trend toward hosted IP telephony for business phone systems is demanding changes in music on hold message technology. In November, 2013, EasyOnHold.com introduced custom messages on hold streams for use with Asterisk and OnSIP phone systems.Wikipedia - Music On Hold
Note, IPitomy, which uses the SIP standard, randomly assigns RTP ports in the range of 10,000-20,000. The music on hold stream should avoid using ports in that range.
All music on hold must be properly licensed, either through the appropriate Performing Rights Organization in your country, or a licensed provider, such as Easy On Hold®. Beware of your licensing liabilities before putting music on hold.