Wrong on two counts, the first being that SMS messages are 160 characters, Twitter is 140, the second being that SMS is only used for sending requests, the real data arrives via MMS.
PanMan
By default SMS is 160 characters, but only in the default 7 bit encoding. It's 160*7 bits (of content), which is actually 140 chars in 8 bits.
I guess it depends on your type of characters :)