自定义的函数如下（这个是测试可用的）：

$agent = check_wap();
    if( $agent )
{
    header('Location: http://www.baidu.com');
    exit;
}
// check if wap
function check_wap(){
    // 先检查是否为wap代理，准确度高
    if(stristr($_SERVER['HTTP_VIA'],"wap")){
            return true;
        }
        // 检查浏览器是否接受 WML.
        elseif(strpos(strtoupper($_SERVER['HTTP_ACCEPT']),"VND.WAP.WML") > 0){
        return true;
   }
   //检查USER_AGENT
   elseif(preg_match('/(blackberry|configuration\/cldc|hp |hp-|htc |htc_|htc-|iemobile|kindle|midp|mmp|motorola|mobile|nokia|opera mini|opera |Googlebot-Mobile|YahooSeeker\/M1A1-R2D2|android|iphone|ipod|mobi|palm|palmos|pocket|portalmmm|ppc;|smartphone|sonyericsson|sqh|spv|symbian|treo|up.browser|up.link|vodafone|windows ce|xda |xda_)/i', $_SERVER['HTTP_USER_AGENT'])){
        return true;           
    }
    else{
        return false;  
   }
}

再来一个从PHP框架剥离的判断是否为手机移动终端的函数（这个没测试）：

<?php 
 
function is_mobile_request(){  
    $_SERVER['ALL_HTTP'] = isset($_SERVER['ALL_HTTP']) ? $_SERVER['ALL_HTTP'] : '';  
    $mobile_browser = '0';  
    if(preg_match('/(up.browser|up.link|mmp|symbian|smartphone|midp|wap|phone|iphone|ipad|ipod|android|xoom)/i', strtolower($_SERVER['HTTP_USER_AGENT'])))  
        $mobile_browser++;  
    if((isset($_SERVER['HTTP_ACCEPT'])) and (strpos(strtolower($_SERVER['HTTP_ACCEPT']),'application/vnd.wap.xhtml+xml') !== false))  
        $mobile_browser++;  
    if(isset($_SERVER['HTTP_X_WAP_PROFILE']))  
        $mobile_browser++;  
    if(isset($_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') !== false)  
        $mobile_browser++;  
    // Pre-final check to reset everything if the user is on Windows  
    if(strpos(strtolower($_SERVER['HTTP_USER_AGENT']), 'windows') !== false)  
        $mobile_browser=0;  
    // But WP7 is also Windows, with a slightly different characteristic  
    if(strpos(strtolower($_SERVER['HTTP_USER_AGENT']), 'windows phone') !== false)  
        $mobile_browser++;  
    if($mobile_browser>0)  
        return true;  
    else
        return false;  
}