Patent ID: 8706111

Claim:
A method of performing an attach procedure, comprising: a user equipment performing a first attach procedure by camping on a first public land mobile network (PLMN) using a first radio access technology (RAT); the user equipment performing a second attach procedure by camping on the first PLMN using a second RAT when receiving a first attach reject message associated with a first reject cause from the first PLMN in response to the first attach procedure; the user equipment performing a third attach procedure by camping on a second PLMN using a third RAT when receiving a second attach reject message associated with a second reject cause from the first PLMN in response to the second attach procedure; and the user equipment determining that a packet switch (PS) service fails to be supported when receiving a third attach reject message associated with a third reject cause from the second PLMN in response to the third attach procedure.