CDMA also has optional timer-based registration, with intervals between ~12 sec and ~55 hours (depending on what the base station wants; search 3gpp2 C.S0005 fo

CDMA also has optional timer-based registration, with intervals between ~12 sec and ~55 hours (depending on what the base station wants; search 3gpp2 C.S0005 for REG_PRD for the gory details), or the base station can send a Registration Request Order message (which does what you might expect) to the phone of interest.