Nice work;
btw, i would replace
VALID_IMSI=XXXXXXXXXXX
by
VALID_IMSI=`dbus-send --system --type=method_call --print-reply --dest=com.nokia.phone.SIM /com/nokia/phone/SIM Phone.Sim.get_imsi | head -2 | tail -1 | tr -s '"' ' ' | cut -d ' ' -f 3`