GSM standards specify the length of an SMS messages may only be 160 bytes (7 bit encoding) or 140 bytes (8 bit encoding). You can, however, split a longer message across multiple SMS messages.

Concatenation of SMS messages is necessary when the size of the message (UDH and text) exceeds the capacity of a single SMS message.

SMS concatenation is often used when sending logos and ringtones due to the length of the binary SMS that is created for the delivery and the sequence of the SMS messages is critical for the receiving device to collate the SMS into a single block of data.