the frequency band you gave (88-108) is commercial FM.
if you are building a fm related project, you can use any frequency for your transmitter/reciever.
FM commercial Broadcasting is limited to 88MHz to 108 MHz, but FM [Frequency Modulation] is used in alot of other bands.
You can use low power FM in that band, limited to a few hundred milliwatts without a license. All you would need is a quiet spot in the band. 47CFR covers the Telecommunications rules, commonly called the FCC rules and regulations.
You can get a copy of the frequency allocation chart in pdf format.
Land mobile services tend to use the band below 88Mhz, and Aircraft use the band above 108Mhz. Many countrys also put a limitation on output power and transmitter specs near the edges of the FM band (especially at the aircraft band end) to reduce the chances of interference to these services.