Sorry but it is not hard at all to go over 2gigs on your phone I avg about 3 per month.
Do you stream music a lot? Otherwise you must surf an ungodly amount, because I get a fair amount of email and some light surfing, even some navigation, and hit maybe 300megs a month for that. I will go 500megs-1gig depending on how much Pandora I play.
Like I said, the average was 400megs, might be a bit higher now and note how you and your girlfriend 8-12X that skew the averages.