For email, you should be fine. Like above post said, you have 30MB per day.
For push notification, it is just a few text, very low bandwidth, don't need to turn it off.
There is a problem with your 1GB limit when you browse tons of pictures or view youtube or FB video on daily basic. Video is really the killer, a few minutes of youtube/FB video can easily takes 20MB-50MB. NEVER view video if you don't want a bill shock or view it only when you are using wifi.

This post has been edited by w143: Nov 9 2010, 05:33 PM