If you're viewing in the mobile skin but put the direct URL to the forum you want (or the MyFlyerTalk screen, for that matter), even if you cannot navigate to it using the mobile skin, the page you want will load in the mobile skin.

Here's what I'd do:

1. Exit the mobile skin using the applicable link when viewing a page in the mobile skin
2. Navigate to the forum you want using the regular interface
3. Bookmark it (for future reference)
4. Repeat steps 2-3 for all forums you regularly visit (and the MyFlyerTalk page, if you use that)
5. Go to http://m.flyertalk.com (to re-enter the mobile interface)
6. Access your bookmarks and tap the forum
7. You should enter that forum in the mobile interface.

Alternatively, you can make sure you're subscribed to the forums you want to visit (with or without email notification; doesn't matter) and then simply bookmark the MyFlyerTalk page (http://www.flyertalk.com/forum/usercp.php--a good one to memorize, anyway). Your subscribed forums will all be visible there.