A default (GSM7) encoded message can have a length of max 160 characters. If you put more characters in, the message will be split up into several parts. This kind of message is called long messageor concatenated message. Each part can of a concatenated message can consist of 153 characters at max. This shorter amount is due to the fact, that the other 7 characters are “eaten up” by informational bytes which tell the end user device that its a concatenated message and further information, like total part count, current part count, etc…