Jose wrote:

It's an FCC rule, designed to avoid overloading the old style analog
cell sites. The rule is thought not to apply to the newer digital
cell service (but I don't think it's been tested in court).

It's never going to be tested in court because the FCC regulations explicitly
state that you may legally use PCS phones in the air. One problem there is that
most PCS phones still fall back on the old AMPS frequencies when they can't
connect over the higher frequencies.

George Patterson
The desire for safety stands against every great and noble enterprise.