• Character Encoding: GSM-7 is a 7-bit character encoding standard used for SMS text messaging in GSM networks. It was designed to optimize the use of the limited data payload of SMS messages, which is 160 characters.

• Character Set: The GSM-7 character set includes letters (both uppercase and lowercase), numbers, basic punctuation marks, and certain special characters. It encompasses most characters used in English and some additional European characters.

• Extended GSM-7 Character Set: There is an extended GSM-7 character set that includes additional special characters. Using any character from this extended set reduces the maximum length of a message to 153 characters as it requires an escape character before the extended character.

• Fallback to UCS-2: If a text message contains even a single character outside the GSM-7 character set, the entire message must be encoded using UCS-2, which can significantly reduce the number of characters available per message.

Understanding GSM-7 is important for optimizing SMS content, especially in applications or services where the number of characters is a critical consideration, such as marketing or notification services.