鸣谢紫殇！
$agent = strtolower($_SERVER[
'HTTP_USER_AGENT']);
$iphone = (strpos($agent, 'iphone')) ? true : false;
$ipad = (strpos($agent, 'ipad')) ? true : false;
$android = (strpos($agent, 'android')) ? true : false;
if($iphone || $ipad){
echo 'you phone is iPhone or iPad';
}else if($android){
echo 'you phone is android';
}else{
echo 'you phone is Windows or Linux or other';
}


法2，感谢学c

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;
}
}
if(check_wap()){
include 'wapcss.css';
}else{
include 'webcss.css';
}