SMS is actually 140 octets, but the GSM 7-bit encoding that's typically used means you can get 160 characters. If you use characters outside that set, its switc

SMS is actually 140 octets, but the GSM 7-bit encoding that's typically used means you can get 160 characters. If you use characters outside that set, its switches to 16-bit UCS-2 so you are limited to 70 characters. In reality you can send messages longer than this and they will be split into multiple messages over the wire - however in the US where you had (have?) to pay to receive messages it meant you would be charged for each individual message. TL;DR; These limits may have made sense for the MVP, but as soon as most people moved to IP clients they were obsolete.