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A Unicode SMS refers to SMS messages sent and received containing characters not found in the GSM-7 character set. An SMS allows up to 160 characters

Unlike English SMSes, the length of regional languages is calculated based on the space the text occupies. This could vary from 2 to 3 characters. The easiest way to figure this out is to paste the SMS in the Exotel SMS dialogue box and you can see the number of characters that will be displayed.

If the message contains even a single Unicode character, the entire message will have to be converted into Unicode. The maximum length of a Unicode SMS is 70 characters per SMS.

For example, this SMS is 90 characters long and will be charged as 2 SMS. 

Note: Unicode SMSes take up more space compared to traditional SMSes.

All Regional languages are sent with Unicode characters. Also, special characters like " - the double quote are included in the Unicode text

You can also refer to the next article on How is the length of an SMS calculated