I figured this out the other day and thought it would be a good idea to pass on. SMS messages are just sent to special email addresses, so they can be sent from server to phone with minimal effort. Here is the form and handler, feel free to copy or modify it in any way you see fit:

The form:
Code:
<form id="sms" name="sms" method="post" action="scripts/send_sms.php">
<table width="400">
  <tr>
    <td align="right" valign="top">From:</td>
    <td align="left"><input name="from" type="text" id="from" size="30" /></td>
  </tr>
  <tr>
    <td align="right" valign="top">To:</td>
    <td align="left"><input name="to" type="text" id="to" size="30" /></td>
  </tr>
  <tr>
    <td align="right" valign="top">Carrier:</td>
    <td align="left"><select name="carrier" id="carrier">
      <option value="verizon">Verizon</option>
      <option value="tmobile">T-Mobile</option>
	  <option value="sprint">Sprint</option>
	  <option value="att">AT&amp;T</option>
	  <option value="virgin">Virgin Mobile</option>
    </select></td>
  </tr>
  <tr>
    <td align="right" valign="top">Message:</td>
    <td align="left"><textarea name="message" cols="40" rows="5" id="message"></textarea></td>
  </tr>
  <tr>
    <td colspan="2" align="right"><input type="submit" name="Submit" value="Submit" /></td>
    </tr>
</table>
</form>
The handler:
Code:
<?php
$from = $_POST['from'];
$to = $_POST['to'];
$carrier = $_POST['carrier'];
$message = stripslashes($_POST['message']);

if ((empty($from)) || (empty($to)) || (empty($message))) {
header ("Location: sms_error.php");
}

else if ($carrier == "verizon") {
$formatted_number = $to."@vtext.com";
mail("$formatted_number", "SMS", "$message"); 
// Currently, the subject is set to "SMS". Feel free to change this.

header ("Location: sms_success.php");
}

else if ($carrier == "tmobile") {
$formatted_number = $to."@tomomail.net";
mail("$formatted_number", "SMS", "$message");

header ("Location: sms_success.php");
}

else if ($carrier == "sprint") {
$formatted_number = $to."@messaging.sprintpcs.com";
mail("$formatted_number", "SMS", "$message");

header ("Location: sms_success.php");
}

else if ($carrier == "att") {
$formatted_number = $to."@txt.att.net";
mail("$formatted_number", "SMS", "$message");
header ("Location: sms_success.php");
}

else if ($carrier == "virgin") {
$formatted_number = $to."@vmobl.com";
mail("$formatted_number", "SMS", "$message");

header ("Location: sms_success.php");
}
?>
Sending a text message to a cell phone through PHP is just a matter of appending the correct suffix to the number and using the mail() function. If you want to add more carriers, go here and find the carrier you are looking for. If you do not know the carrier (ie. if you want to add a "not sure" option to the pulldown menu), add @teleflip.com as the suffix. The phone numbers must be 10 digits long (XXX-XXX-XXXX).

Feel free to contact me if you are having any trouble,
The Yembo Project