Abstract: A method and apparatus controls zone registrations in a radio communication system providing radio coverage to a portable subscriber unit (122) within a plurality of zones (402), wherein the portable subscriber unit (PSU) determines its own call rate (602). A fixed portion (102) of the radio communication system sends the PSU a threshold value based on communication activity associated with the PSU, a call rate estimation interval value, and a multiplier for normalizing the PSU's own call rate with the threshold value. The fixed portion accepts zone registrations from the PSU when the PSU's own call rate is greater than the threshold value and defers zone registration from the PSU when the PSU's own call rate is less than or equal to the threshold value until the PSU's own call rate exceeds the threshold value.