Viktor Szépe

Enables users with <code>list_users</code> capability (Editors and Administrators) 
to send plain text message to any user in an email.
There is a new action “Send message” provided on the Users admin page 
for each user.

Send message

Send an email (subject and text message) to WordPress users.

Mostafa Soufi

The SMS via wordpress very easy
Features:
<ul>
<li>Send SMS to number and numbers</li>
<li>Send SMS to subscribes</li>
<li>Subsribe sms</li>
<li>Show credit</li>
<li>Send SMS via FLASH</li>
<li>Widget support</li>
<li>Support shortcode</li>
<li>Support suggestion post by SMS.</li>
<li>Send activation from subscribe.</li>
<li>Notification of a new wordPress version by SMS (New)</li>
</ul>

Send message vs Hostiran SMS Plugin