[cesarb]

> decided on the limit after typing up a bunch of sample sentences

From what I heard, the SMS limit was actually a protocol limitation: it piggybacks on signaling messages, which have a small size limit (this is also why SMS can sometimes work even when everything else doesn't). Quoting from Wikipedia (https://en.wikipedia.org/wiki/SMS):

"Messages are sent with the MAP MO- and MT-ForwardSM operations, whose payload length is limited by the constraints of the signaling protocol to precisely 140 bytes (140 bytes * 8 bits / byte = 1120 bits). Short messages can be encoded using a variety of alphabets: the default GSM 7-bit alphabet, the 8-bit data alphabet, and the 16-bit UCS-2 alphabet. Depending on which alphabet the subscriber has configured in the handset, this leads to the maximum individual short message sizes of 160 7-bit characters, 140 8-bit characters, or 70 16-bit characters."