Archived from groups: alt.cellular.gsm (More info?
> why sms is only 160 characters long?
Because an SMS can use either a 7-bit, 8-bit or 16-bit alphabet,
the number of bytes needs to be even and a factor of 7 (to
avoid wasted space).
To achieve the elegance of having a number that's a multiple of
10, the choices get further limited to 70, 140, 210, 280, etc
bytes. I can only assume the choice of 140 bytes (160 7-bit
characters) was made over 210 bytes (240 7-bit characters)
because it seemed to be the best compromise between usefulness
and available resources.