On hold music has been around for almost as long as the phone system itself. It is a nice way to try and delight callers while calls are being routed especially when it's a busier than normal time and call times tend to extend.
It's not unusual for companies to pay for a personalized on hold music file to be created with pop ins for things such as products, services, tips, and so on. What most don't know is that when you pay for a customize on hold music file to be created for your orginization part of that fee covers the license to use the music that is playing in the background.
When you buy a song on iTunes or rip a file from a CD that music was licensed for you to use personally and not in a public format. Radio stations, film makers, sports stadiums, for example have to pay royalties every time a music is played.
The same applies to phone systems too. I know it's easy to upload that Christmas song, catchy song you just heard on your car radio or TV commercial however you would be putting yourself at risk by using that same music for your phone system on hold music.
You can learn all about how the music industry makes their money here.
The trick here is to search for Royalty Free Music which means that if you use it in a public format nobody will come asking for you to pay a license to do so.
A quick Google search show plenty of options!
Other examples of sites that have plenty of royalty free music to choose from are:
http://www.smartsound.com/blog/royalty-free-on-hold-music.html
http://www.beatsuite.com/music/category/royalty-free-hold-music/642
Don't get caught unexpectedly with a demand letter to pay for music because you were quick to upload music and didn't realize that you are not just allowed to use it for your phone system!