How to redirect mobile style to a subdomain?

Basically, I've installed the premium mobile suite for vBulletin and I want the mobile users to be redirected to mobile.forum.com instead of www.forum.com. Now, I've seen that I need to redirect the styleid but I don't know if I need to add something to vbseo or how do I do it. I have both vBCMS and forum (the publisher suite). The site root is the CMS.

If I go to www.site.com/?styleid=2 for example, it doesn't go to the style 2.

Any advice is appreciated.

Multiple domains are not supported. You can use mobile.site.com to point to www.site.com?styleid=2 if you wish, but it is not possible to USE mobile. as the actual url.

Assuming the mobile subdomain points to the same public_html/ area as your forum (you can configure this at your host level) You can use something like

RewriteCond %{HTTP_HOST} ^mobile\.yourdomain\.com$
RewriteRule (.*) http://www.yourdomain.com/$1?styleid=2 [L,R=301]

Above your main non-www to www rule in htaccess.

If styleid=2 doesn't re-direct you, you need to consult vb support for that.

actually, it's the opposite. when a user enters on my site on his mobile, they are detected and redirected to styleid=2, so basically, I need to redirect www.site.com?styleid=2 to m.site.com. Does it work the other way around?

As stated, this is not possible.