I've been having some problems trying to use my phone (Nexus 4) as well. I can use the menus on one of the browsers I use (UC Browser), but can't even log in. Other browsers won't even let me use the menus or log in at all.
I finally got logged in using Opera Mini, but of course the whole layout is 100% broken from using it. I tried sending a PM earlier using Opera Mini, and got told I can't send to that user group for some reason.
The only users that show in the userlist for sending a PM are the Administrators & Moderators. Apparently the antispam mod is blocking me from sending a PM because of my low post count, but it should go through if you're allowed to use that function. I'm not sure about submitting panels or anything else like that though.
EDIT: I am able to post using Opera Mini, but its a hassle to uncheck the box to be notified of replies, and sometimes you have to retype your post because it gets cleared from the text box. Hmm...