How do I send a text (SMS) message from Messenger?

Send text messages to friends who use any of the wireless carriers listed in this article, "What are the supported wireless carriers for text messaging?."
Here are three ways to start a text message. (Choose what's easiest!)

1. Click the Actions menu in Yahoo! Messenger and select Send an SMS Message.
2. Right-click the contact from the Messenger List and select Send an SMS Message.
3. Click the text message icon in the address book.

OK, now enter your friend's mobile phone number. Make sure you add the country code for International numbers.
Country codes:
USA +1
Canada +1
India +91
Singapore +65
Thailand +66
Malaysia +60
Philippines +63

Type your message and click Send.
Note: To use the right-click menu or Address Book icon, you must have a mobile number listed in the Contact Details for that person.