There are two major frequencies used by carriers in the United States and Canada. They are 800MHz and 1900MHz.
Many of the cell phones sold are multi-frequency so you can roam from location to location. The website www.wirelessadvisor.com has carrier and frequency information that can be accessed by zip code.
Sometimes carriers operate on 800MHz for voice and 1900MHz for data. Many phones have both voice and data capabilities.
It is best when purchasing a mobile amplifier to get a dual-band system. This allows you to use any phone on any carrier. It also helps protect your investment in case you happen to switch phones or carriers in the future.
It is always best to consult with your carrier to acquire this information.