Unable to access Yelp account on 3G network but on WIFI

I'm not sure if anyone can help me on this. I can't access my Yelp account on the AT&T 3G network. I can't access it from either the app itself or if I attempt to use the browser. On the browser, I just get the error message that I've entered an invalid email and/or password when I haven't. I can only seem to access my account when I'm on a WIFI network. Anyone else experiencing this or is it just me? What can I do? I've contacted Yelp & of course they'll get back to me within a week. Just great! :p