There are actually relatively few frequencies they could be using. If you were to try this I would look into the commercial VHF band as that is most likely where they are, or the UHF band.
For a bit more info look here
http://en.wikipedia.org/wiki/Business_band
If you want to learn more about radio, check out the American radio relay league about becoming an amateur radio operator.
For the teams that cannot use their cell phones in the US, look into the cheap (approx $20 US) prepaid cell phones, they would likely do what you want and are not disallowed.