nsa said:
why sms is only 160 characters?
Because it is a hack:
Some unknown (to me anyway) engineer got the idea to stick ascii text into
the unused bits of the location update messages that the mobile terminal
exchanges with the basestation - it was probably implemented because the
routing of location updates was already in the network and thus free - and
then the teenagers decided it was cool...
the unused bits just happened to hold 160 Ascii chars.