When the type of network is HSPA, the indication is certainly valid
during traffic, while it could be not valid in idle because it depends
on network broadcast parameters.
AT#PSNT?
If <mode> is set to 0 or 1, read command returns the current values of the
<mode> and <nt> parameters in the format:
#PSNT: <mode>,<nt>
If <mode> is set to 2, read command returns the current values of <mode>
and <nt> parameters followed by four dummy parameters set to 0.
#PSNT:<mode>,<nt>,0,0,0,0