Code for a basic SMS voting system. Full write-up here: http://www.twilio.com/blog/2011/05/how-to-create-a-simple-sms-voting-system-using-php.html

db.php

<?php
	class DB {
		const DB_NAME = 'votes.sqlite';

		protected $db;

		function __construct() {
			$this->db = new PDO('sqlite:'.self::DB_NAME);
		}

		function init() {
			// Create two tables, one to store the teams being voted on and their vote counts (teams) and one to store the people that have voted (voters).
			$this->db->exec('CREATE TABLE IF NOT EXISTS teams (id INTEGER PRIMARY KEY, name TEXT, votes INTEGER);');
			$this->db->exec('CREATE TABLE IF NOT EXISTS voters (id INTEGER PRIMARY KEY, phone_number TEXT, voted_for INTEGER);');
		}

		function add_team($name) {
			// Check to make sure the team name doesn't already exist
			$stmt = $this->db->prepare('SELECT COUNT(*) FROM teams WHERE name=?');
			$stmt->execute(array($name));

			// If not, insert it
			if ($stmt->fetchColumn() == 0)
			{
				$stmt = $this->db->prepare('INSERT INTO teams (name, votes) VALUES (?, 0)');
				$stmt->execute(array($name));
			}
		}
		
		function get_teams() {
			$result = $this->db->query('SELECT * FROM teams');

			foreach ($result as $row)
			{
				$team['id'] = $row['id'];
				$team['name'] = $row['name'];
				$team['votes'] = $row['votes'];

				$teams[] = $team;
			}

			return $teams;
		}
		
		function save_vote($phone_number, $voted_for) {
			// Just the digits, please
			$phone_number = preg_replace('/\D/', '', $phone_number);
			
			// Check to see if person has already voted
			$stmt = $this->db->prepare('SELECT COUNT(*) FROM voters WHERE phone_number=?');
			$stmt->execute(array($phone_number));

			// If not, save their vote
			if ($stmt->fetchColumn() == 0)
			{
				// Save voter
				$stmt = $this->db->prepare('INSERT INTO voters (phone_number, voted_for) VALUES (?, ?)');
				$stmt->execute(array($phone_number, $voted_for));

				// Update vote count
				$stmt = $this->db->prepare('UPDATE teams SET votes = votes + 1 WHERE id=?');
				$stmt->execute(array($voted_for));

				return 'Thank you, your vote has been recorded';
			}
			else {
				return 'Sorry, you can only vote once.';
			}
		}
	}
?>

display-votes.php

<?php
	require_once('db.php');

	$db = new DB();

	// Grab all the teams (and their vote counts) from the database
	$teams = $db->get_teams();

	echo '<ul>';

	// Loop through each team and display how many votes they got
	foreach ($teams as $team)
	{
		echo '<li>'.$team['name'].': '.$team['votes'].' votes</li>';
	}

	echo '</ul>';
?>

handle-incoming-sms.php

<?php
	require_once('db.php');

	header('Content-type: text/xml');
	echo '<Response>';

	$phone_number = $_REQUEST['From'];
	$team_number = (int) $_REQUEST['Body'];

	// If we've got good data, save the vote
	if ( (strlen($phone_number) >= 10) && ($team_number > 0) )
	{
		$db = new DB();

		// save_vote will check to see if the person has already voted
		$response = $db->save_vote($phone_number, $team_number);
	}
	else {
		// Otherwise, give the user an example of how to vote
		$response = 'Sorry, I didn\'t understand that. Text the team number to vote. For example, texting 1 will vote for Team 1.';
	}

	// Send an SMS back to the person that voted letting them know that their vote was saved, or that there was an error of some sort
	echo '<Sms>'.$response.'</Sms>';
	echo '</Response>';
?>

setup.php

<?php
	// Sets up the database. Only needs to be run once. After that you can delete this file.
	require_once('db.php');

	$db = new DB();

	// Create the database tables
	$db->init();

	// Add some teams
	$db->add_team('Team 1');
	$db->add_team('Team 2');
	$db->add_team('Team 3');

	echo 'Database created and teams added';
?>