php怎么判断手机客户端访问？

// check if wap
function check_wap(){
    if(stristr($_SERVER['HTTP_VIA'],"wap")){// 先检查是否为wap代理，准确度高
        return true;
    }elseif(strpos(strtoupper($_SERVER['HTTP_ACCEPT']),"VND.WAP.WML") > 0){// 检查浏览器是否接受 WML.
        return true;
   }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'])){//检查USER_AGENT
        return true;
    }else{
        return false;
   }
}