I had wifi at home but not at work, and looked at facebook, DW, etc on my phone pretty regularly for my ~45 minute commutes, during lunch, etc, and I also used google maps a fair amount. I rarely used 500 MB per month. Streaming video and tumblr ate through my data though.

(I'm using past tense because I now have an iphone and I haven't figured out how to see what my data usage is. I'm not worried about it though.)

The HTC One, another android phone, is also very good. I had it before the iphone and liked it a lot.