1) I'm unclear what I'm supposed to enter on the plan details screen's "billing date".
My last bill covered 2012-12-10 through 2013-01-09. Do I enter 9 or 10 there? Experimenting, it looks like you want the first day in the next bill, so 10.
2) The time on network graph is showing a lot of time on 3g, but that's because the phone is on WiFi so it dropped the HSDPA+ connection, probably to save power. Would be nice if you could exclude when on WiFi from that chart.