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"Short Message Service (SMS), often called text messaging, is a means of sending short messages to and from mobile phones." (Wikipedia)
SMS messages can be of 160 ASCII characters. When non-ASCII characters (such as Latin extended characters) are used, the message length is restricted to 70. [need more info - there was a discussion on the Unicode mail list about this beginning 2006/5/28]
In principle one type text messages in any language with a basic ASCII characters, provided the workarounds or transliterations are understood by the receiver.
Archives of the Unicode Mail List http://www.unicode.org/mail-arch/
Wikipedia, "Short message service," http://en.wikipedia.org/wiki/Short_message_service