It might seem like Twitter's length limit is due to SMS but it's actually not.
Twitter's limit is 140 Unicode characters, which is subtly different from SMS's limit of 140 bytes (160 7-bit characters or 70 UTF-16 characters).
Twitter's limit is 140 Unicode characters, which is subtly different from SMS's limit of 140 bytes (160 7-bit characters or 70 UTF-16 characters).
Twitter's limitation is based on thinking around SMS, but it doesn't actually match up to real world SMS, because they didn't think through all the international language considerations. It's pretty botched up.