
Create a new text message using any of these actions...
click the New Message button in the Message Center toolbar
select New Message (⇧⌘N) from the File menu, a device menu, or a phonebook token menu
select Forward (⇧⌘F) or Reply (⇧⌘R) from the Message Center or the Message View Window
type a HotKey set up in the HotKeys Preferences
The window toolbar contains Save, Send, Export and other buttons. The toolbar can be modified by control-clicking (right-clicking) on the toolbar and selecting Customize Toolbar.

Use the address field to add contacts. Group names and multiple entries are supported.
Select the device to use to send the message from the Device popup menu.
Enter your message into the text field.
The SMS Character Counter displays information on the length of your message that you may find useful if you are charged per-text message.
To send the text message, click the Send button in the window toolbar, or select Send (⇧⌘D) from the Messages menu.
Sent messages are stored on your computer by default (and not in your phone's sent folder) in order to preserve accurate message dates. To change this option, visit the Message Center Preferences.
Phone-specific settings (such as Status Reports and SMSC Address) are available in the SMS Delivery Options.