The following information was published from the Part 15 Lab Blog. From 2002 - 2004 I operated a Part 15 station and I got the proper music licensing. The fact is that if you are broadcasting music to the public, you have to obtain the proper music licensing. The article below will discuss the details.
If you are publicly broadcasting licensed, copyrighted music, regardless if yours is a licensed station, a Part 15 unlicensed station, or a bar room jukebox, you are required to obtain a license, pay the fees for the rights, and provide periodic logs (this is a touchy subject for some who disagree).
For Part 15 stations, a license is obtainable from BMI at www.bmi.com/licensing/entry/radio; The contract is predominately displayed on the right menu, entitled "BMI Part 15 Station Radio License". It is a 5 page contract which you are required to fill out and return with payment.
A few excerpts from the BMI Contract: