mod_rewrite_rules

RewriteEngine On

# If the user is asking for the fullsite, set a cookie, remove the query, and stop.
RewriteCond %{QUERY_STRING} ^fullsite$
RewriteRule ^/?(.*)$ http://domain.com/$1? [L,CO=fullsite:yes:.domain.com]

# If the user is asking for the mobilesite, set a cookie, remove the query, redirect and stop.
RewriteCond %{QUERY_STRING} ^mobilesite$
RewriteRule ^/?(.*)$ http://m.domain.com/$1? [L,CO=fullsite:no:.domain.com] 

# If the visit is from a mobile user agent, and there's no fullsite cookie, redirect and stop
# if the browser accepts these mime-types, it's definitely mobile, or pretending to be
RewriteCond %{HTTP_ACCEPT} "text\/vnd\.wap\.wml|application\/vnd\.wap\.xhtml\+xml" [NC,OR]
# a bunch of user agent tests
RewriteCond %{HTTP_USER_AGENT} "sony|symbian|nokia|samsung|mobile|windows ce|epoc" [NC,OR]
RewriteCond %{HTTP_USER_AGENT} "mini|nitro|j2me|midp-|cldc-|netfront|mot|up\.browser|up\.link|audiovox"[NC,OR]
RewriteCond %{HTTP_USER_AGENT} "ericsson,|panasonic|philips|sanyo|sharp|sie-"[NC,OR]
RewriteCond %{HTTP_USER_AGENT} "portalmmm|blazer|avantgo|danger|palm|series60|palmsource|pocketpc"[NC,OR]
RewriteCond %{HTTP_USER_AGENT} "smartphone|rover|ipaq|au-mic,|alcatel|ericy|vodafone\/|wap1\.|wap2\.|iPhone|android"[NC,OR]
RewriteCond %{HTTP_USER_AGENT} "android|blackberry|iphone|ipod|iemobile|opera mobile|palmos|webos|googlebot-mobile" [NC]
# Note: I've updated the conditions above to skip iPads. However,
# mobile safari still reports itself as 'mobile' and thus needs an explicit opt-out
RewriteCond %{HTTP_USER_AGENT} !iPad [NC]
RewriteCond %{HTTP_COOKIE} !^.*fullsite=yes.*$ [NC]
RewriteRule ^/?(.*)$ http://m.domain.com/$1 [L,R=302]