Can One simply make an ordinary m.domain.com subdomain after which in some way use .htaccess to redirect/rewrite it towards the tld?

I am using Wordpress and all sorts of I is going to do at that time is identify if there's a m. subdomain and show a mobile template rather than the standard site.

Is dependent the way you setup the VirtualHosts. For those who have setup your server in ways which means it uses exactly the same VirtualHost, using either ServerAlias (as pointed out by Gerben), or because of it being the only real or default VirtualHost. Once both are striking exactly the same files the mod_rewrite ought to be quite simple. I am presuming you would like it to make a move slightly dissimilar to the tld, hence the various domain title, so we'll assume you want to pass through around the information it's mobile...

RewriteCond %{HTTP_HOST} ^m.tld.com$
RewriteRule .* %{REQUEST_URI}?mobile=true [QSA]