http://stackoverflow.com/questions/1...-with-htaccess

RewriteCond %{HTTP_HOST} ^m\. [NC]
RewriteCond %{HTTP_USER_AGENT} !(android|blackberry|googlebot-mobile|iemobile|iphone|ipod|opera\smobile|palmos|w ebos) [NC]
RewriteRule ^ http://website.com%{REQUEST_URI} [L,R=302]