System identification (SID) list for selecting operating frequencies

摘要

A cellular telephone system is upgraded by modifying subscriber units for selective service provider acquisition during roaming. Priority of acquisition is given to those service providers associated with the home service provider. These preferred service providers are identified by System Identification (SIDs) numbers. A roaming subscriber unit will tune to control frequencies to identify all of the system providers operating in a physical area to which the subscriber has roamed. The SIDs of those system providers available are compared to a list contained within the subscriber unit. Selection is made based upon a priority of those system providers having arrangements with the home system provider.