This simple lightweight piece of code developed by Andy Moore and modified by Mobiforge allows you to redirect your users through to a mobile version of your site. The best way to do this would be to include the following code into the top of the index page as this is most likely your first point of entry. It is advised as i did in the iphone detection tutorial found here to give users the option on mobile pages to view the original site.

<?php

$mobile_browser = '0';

if(preg_match('/(up.browser|up.link|mmp|symbian|smartphone|midp|wap|phone)/i', strtolower($_SERVER['HTTP_USER_AGENT']))) {
    $mobile_browser++;
}

if((strpos(strtolower($_SERVER['HTTP_ACCEPT']),'application/vnd.wap.xhtml+xml')>0) or ((isset($_SERVER['HTTP_X_WAP_PROFILE']) or isset($_SERVER['HTTP_PROFILE'])))) {
    $mobile_browser++;
}    

$mobile_ua = strtolower(substr($_SERVER['HTTP_USER_AGENT'],0,4));
$mobile_agents = array(
    'w3c ','acs-','alav','alca','amoi','audi','avan','benq','bird','blac',
    'blaz','brew','cell','cldc','cmd-','dang','doco','eric','hipt','inno',
    'ipaq','java','jigs','kddi','keji','leno','lg-c','lg-d','lg-g','lge-',
    'maui','maxo','midp','mits','mmef','mobi','mot-','moto','mwbp','nec-',
    'newt','noki','oper','palm','pana','pant','phil','play','port','prox',
    'qwap','sage','sams','sany','sch-','sec-','send','seri','sgh-','shar',
    'sie-','siem','smal','smar','sony','sph-','symb','t-mo','teli','tim-',
    'tosh','tsm-','upg1','upsi','vk-v','voda','wap-','wapa','wapi','wapp',
    'wapr','webc','winw','winw','xda','xda-');

if(in_array($mobile_ua,$mobile_agents)) {
    $mobile_browser++;
}

if (strpos(strtolower($_SERVER['ALL_HTTP']),'OperaMini')>0) {
    $mobile_browser++;
}

if (strpos(strtolower($_SERVER['HTTP_USER_AGENT']),'windows')>0) {
    $mobile_browser=0;
}

if($mobile_browser>0) {
   // do something
}
else {
   // do something else
}   

?>

Hope you find it useful