Various schemes for performing inter-system handoff, e.g., from a UTRAN to a cdma2000 radio access network (RAN) are described. For a MAHHO scheme, the UTRAN uses measurements obtained by a multi-RAT device to determine suitable cdma2000 cell(s) for handover. The measurements are obtained by a candidate frequency search procedure, and the handover is accomplished by a handoff execution procedure. For a MDHHO scheme, the UTRAN relies on location information for the multi-RAT device to select suitable cdma2000 cell(s) for handover. For a CRHHO scheme, a new call is established on the cdma2000 RAN and the pending call on the UTRAN is released in a manner such that the handover appears seamless to the multi-RAT device. The multi-RAT device includes two modem processors that perform processing for the UTRAN and cdma2000 RAN and an application processor that controls the modem processors.