The Twitter page is pretty neat, but I've noticed that on my LG phone (using Verizon web browser) and my brother's AT&T iPhone browser that ffxiah.com itself comes out very cleanly.
While there are a few exceptions on coding that get tripped up on my mobile's browser (like it doesn't want to render character-homepage transaction tables, individual item transaction tables, or certain functions like [ spoiler ] or the quote link) for the most part everything else comes out fine (i.e. guild pattern tables, linkshell tables, log-in, and all of the forums.)
I think ffxiah.com is already pretty mobile-friendly as it is, at least on the few phones I've tried out.