It is even easier than I thought. If you send the message to ##########@teleflip.com they will forward it to the correct provider. It works, I was bored and threw one together http://texting4free.com Feel free to borrow the source, alot of it is borrowed pieces I found. It is pretty erll commented so you can see how it works.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<title>Texting4Free.com Send test messages for free!</title>
</head>
<body bgcolor="EAEAEE">
<p align="center">
<img border="0" src="/banner.gif" width="468" height="60" alt=""><p align="center">
<div align="center">
<center>
<?php
// Process the form if it was submitted
if (isset($_POST['do'])) {
// Parse the data submitted from the form
$number = trim($_POST['number']);
$subject = trim($_POST['subject']);
$message = trim($_POST['message']);
// Check that the phone number is numeric
if (!is_numeric($number)) {
$error = "Please enter a phone number containing only digits 0-9.";
// Make sure the phone number doesn't start with 911
} elseif (eregi("^(911)(.*)$", $number)) {
$error = "Please enter a valid phone number.";
// Check that the phone number is 10 digits
} elseif (strlen($number) != "10") {
$error = "Please enter a phone number that is 10 digits (the 3 digit area code and 7 digit number).";
// Check that the subject doesn't contain HTML characters
} elseif (eregi("^(.*)(<|>)(.*)$", $subject)) {
$error = "The subject of the message cannot contain HTML characters (such as > or <).";
// Check that the message doesn't contain HTML characters
} elseif (eregi("^(.*)(<|>)(.*)$", $message)) {
$error = "The message cannot contain HTML characters (such as > or <).";
// Check that the subject is between 3 and 20 characters
} elseif ((strlen($subject) < "3") || (strlen($subject) > "20")) {
$error = "The subject must be between 3 and 20 characters in length.";
// Check that the message is between 3 and 120 characters
} elseif ((strlen($message) < "3") || (strlen($message) > "120")) {
$error = "The message must be between 3 and 120 characters in length.";
// Send the message
} else {
// Where are we sending it?
$to = "" . $number . "@teleflip.com";
// Send the text message (via Teleflip's service)
if (@mail($to, $subject, $message)) {
// Give a success notice
echo "Text message sent.";
echo "</center>\n";
echo "</body>\n";
echo "</html>\n";
exit;
// Give an error that message can't be sent
} else {
$error = "Sorry, there was an error while trying to send the message - please try again later.";
}
}
}
// Show any errors encountered
if (isset($error)) {
echo "<font color=\"red\"><b>" . $error . "</b></font><br><br>\n";
}
?>
<form method="POST" action="<?php echo $_SERVER['SCRIPT_NAME']; ?>">
<table border="1" cellpadding="0" cellspacing="0" style="border-collapse: collapse" id="AutoNumber1">
<tr>
<td align="left">
<b>Number</b><br>
<input type="text" name="number" maxlength="10">
</td>
<td align="right">
Enter the recipient's 10 digit phone number. (For example: 8001234567)
</td>
</tr>
<tr>
<td align="left">
<b>Subject</b><br>
<input type="text" name="subject" maxlength="20">
</td>
<td align="right">
Enter a short, brief word or two for the subject of the message.<br>
This must be between 3 and 20 characters in length.
</td>
</tr>
<tr>
<td align="left">
<b>Message</b><br>
<textarea name="message" rows="5" cols="25"></textarea><br>
</td>
<td align="right">
Enter your message.<br>
This must be between 3 and 120 characters in length.
</td>
</tr>
<tr>
<td align="center" colspan="2">
<input type="submit" name="do" value="Send">
</td>
</tr>
</table>
</form><br><br>
<b>Notice:</b> <i>The phone number must be a standard North American 10 digit number (with area code).</i><br>
<i>Also, every text message sent will have a small note on the bottom saying that it was indeed sent via Teleflip's service.</i><br><br>
Message sending provided by <a href="http://teleflip.com">Teleflip</a>.<br>
</center>
<p>
<a href="http://validator.w3.org/check?uri=referer"><img
src="http://www.w3.org/Icons/valid-html401-blue"
alt="Valid HTML 4.01 Transitional" height="31" width="88"></a>
</p>
</div>
</body>
</html>