It turns out that "Modem is [NOT] registered" is not a good indicator
of whether the card has service or not; instead some of the AT!STATUS
response is needed to really determine registration state or not.
at!pcstate is what Sierra CDMA modems use instead of AT+CFUN for
powering the radio on and off. It doesn't turn the modem off completely
like AT+CFUN=0 does for many GSM devices though, so it's quite a lot nicer.
Dan Williams