I'm browsing and posting this on my lappy right now, and http traffic works just fine...
But I just thought about this earlier today: I don't use windows. I am actually using Ubuntu Linux, so maybe the metroPCS block is not whitelisting the R910, but rather blacklisting windows as OS. So if you don't want to be plagued with Mobile versions of websites while trafficking because your user agent appears to come from a phone, try to change the OS to say Linux instead of MS Winblows...
For example, here is my user agent string
Mozilla/5.0 (Ubuntu; X11; Linux x86_64; rv:8.0) Gecko/20100101 Firefox/8.0
and it's working just fine.
Done rambling on... Hope this helped...