How to use iChat to send SMS messages
To send an SMS (text message) from iChat to a cellular phone:
1. Choose New Chat with Person (Shift-Command-N) from the File menu.
2. Enter the cellular phone number where you would typically enter the AIM screen name or the Mac .com account. Use the format: +15551234567
Note: You must use the plus sign (+) first, followed by a 1, the area code, and the seven-digit cellular phone number.
3. Click OK.
4. Type the text of your message and click Return.
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Okay, it makes reference to “the area code, and the seven-digit phone number”, which very likely means it could be limited to the U.S. YMMV.