I know there must be some limit but why 160? Why not 255 which makes more sense? And for all you smartasses out there and nitpickers i do not care that some providers and phones will split the message up for you and send it separately. Why was 160 chosen?
If it’s actually a limit set by the wireless carrier and not the phone, then it might have something to do with the point at which they don’t make enough mon…wait, maybe becuase they’d rather you just sent two messages instead of one.
Probably they’re trying to fit everything into 256 bytes. So with your 160 byte message, that leaves ~100 bytes to include your To email address, From email address, and any other header information. It might be just To and From, since some email addresses can be quite long. 50 bytes for a single address is within the realm of reason.
I think that true text messages just have phone numbers for who sent them and where they’re going. But the point does still make some sense.
Going from this (PDF), the MAP protocol requires enough data that only 160 bytes are left.
Going by the Wikipedia page on SMS, though, it actually looks like there is only enough room for 140 bytes, but English (ASCII) only takes 7 bits so you can fit in 160 characters of it.