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I'm building a grants management system where we're trying to find a list of lost users using a number of different means.

The first attempt is email but if we do not have an email address, we will try SMS.

Just wondering, before we get our business guys to start thinking up SMS messages, is there a maximum length or something which I should stay within to reach every phone with SMS capability?

Taking also in account that whilst we won't be sending an SMS to international numbers, a lot of the users will be from foreign countries and may have a foreign cell phone.

Also, messages will only ever be in English.

2 Answers 2

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All GSM handsets must support the 7 bits alphabet from GSM 03.38. As the payload is 140 bytes, that translates into 160 characters.

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SMS is 140 ascii characters or 70 ut16 characters http://en.wikipedia.org/wiki/SMS#Message_size

Transmission of short messages between the SMSC and the handset is done whenever using the Mobile Application Part (MAP) of the SS7 protocol. Messages are sent with the MAP MO- and MT-ForwardSM operations, whose payload length is limited by the constraints of the signaling protocol to precisely 140 octets (140 octets = 140 * 8 bits = 1120 bits). Short messages can be encoded using a variety of alphabets: the default GSM 7-bit alphabet, the 8-bit data alphabet, and the 16-bit UCS-2 alphabet. Depending on which alphabet the subscriber has configured in the handset, this leads to the maximum individual short message sizes of 160 7-bit characters, 140 8-bit characters, or 70 16-bit characters. GSM 7-bit alphabet support is mandatory for GSM handsets and network elements, but characters in languages such as Arabic, Chinese, Korean, Japanese, or Cyrillic alphabet languages (e.g., Russian, Serbian, Bulgarian, etc.) must be encoded using the 16-bit UCS-2 character encoding...

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  • i had a read of that but it says "Depending on which alphabet the subscriber has configured in the handset, this leads to the maximum individual short message sizes of 160 7-bit characters, 140 8-bit characters, or 70 16-bit characters." Does that mean in some cases, people with certain phones will only receive 70 characters?
    – RoboShop
    Commented Jan 16, 2012 at 6:00
  • That article also says that on GSM, support for its 7-bit character set in SMS is mandatory. So if you can constrain yourself to that, you should be able to use up to 140 characters. I didn't see however a statement that GSM 7-bit is equal to ASCII, so beware of peculiarities in the character set.
    – user
    Commented Jan 16, 2012 at 9:12
  • @MichaelKjörling: It's definitely not ASCII.
    – MSalters
    Commented Jan 16, 2012 at 11:23

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