• Air Canada
  • Panasonic
  • Renault
  • Viber

A standard plain text (7-bit) SMS can contain up to 160 characters.

Note: There are 9 special characters that are counted as 2 individual characters.
See GSM Encoding for more information.

It is possible to send multiple SMS joined together to form a single long message.

This type of message is referred to as any one of the following:

A Long SMS

A Concatenated SMS

A Multipart SMS

An Extended SMS

CLX will always refer to such a message as a Concatenated SMS.

A Concatenated SMS is formed from several standard SMS containing a 7 byte concatenation header at the beginning of each one. Since this 7 byte header is within the message, it reduces the total size of each SMS to 153 characters each.

  • Number of SMSMessage Length

Note: In theory it is possible to utilize 255 messages (39,015 characters) for a Concatenated SMS. However, 3 SMS (or 459 characters), is generally considered to be the longest length message that will be displayed on the majority of mobile handsets. CLX limits Concatenated SMS to 459 characters to ensure maximum compatibility.

Note: Concatenated SMS are billed by the number of individual SMS messages used. If you send a 459 character message, you will be charged for 3 SMS.

CLX will automatically split long messages into the correct concatenated form for most methods of submission.

You only need to split long messages yourself if you are using one of the following protocols to submit SMS:




If you are using one of the above protocols, a brief description of the Concatenation User Data Header can be found below. There are 5 octets required in the User Data Header to describe a Concatenated SMS. These are:


  • Octet NumberValueDescription
    100Information Element Identifier (IEL). Does not change.
    203Information Data Length (IEDL). Does not change.
    3AAA unique hexadecimal reference number. Does change for every set of Concatenated SMS.
    403Total number of Concatenated SMS. Remains the same for each part of a Concatenated SMS.
    501Current Concatenated SMS part number. Does change for every SMS part.

Example UDH’s of a 3 part Concatenated SMS:

0003010301 0003010302 0003010303

Note: Concatenated SMS is not supported by non-GSM networks, or the United States.

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