1 gb / month is criminal. I think my phone easily averages 100 mb a day from the basic processes (mail, whatsapp, light browsing, background app refresh). I often come close to hitting the 3gb data cap (or just exceed it at times).
I have owned my 4S for coming up on three years, and I have yet to hit a grand total of 500MB of data for that entire time period. I have data always turned on, and use it for GPS in addition to all the usual email, iMessage, etc., when out and about. Needless to say, I am on the lowest possible data plan (300MB) and do not see that changing.
A.