Default Is Comcast throttling mobile phones?

I've tried my G2 S3 S4 and an iPod touch. None of them can get above 4mbps. Now my kindle HDX, 1st gen iPad, and laptop can all get the 50 Mbps+. Is it possible that Comcast is actively throttling mobile devices? If so, then why do tablets seem to work fine? If not,then WTF?!

I'm using the supplied new xfinity router out of nessesity. I know that I would be possible to bridge and use my own router, but what gives? Is there even a way for them to do this? I'm not that well versed in networking, but I did try to change the router's broadcasting channel and messed around with the different security protocols. Do you guys have any idea of what's happening and what can be done to remedy this? http://