USER_AGENTを見て判断するサンプル

user_agent.php

<?php

    $userAgent = $_SERVER['HTTP_USER_AGENT'];
    $isMobile = false;

    if (preg_match("/Android/", $userAgent, $match)) {
        $isMobile = true;
    }   

    if (preg_match("/iPhone/", $userAgent, $match)) {
        $isMobile = true;
    }   

    if (preg_match("/iPad/", $userAgent, $match)) {
        $isMobile = true;
    }   

    if ($isMobile) {
        $request->setParam('format','mobile'); 
        define('DEVICE', 'MOBILE');
    } else {
        $request->setParam('format','html'); 
        define('DEVICE', 'PC');
    }