Phone data usage measured in bytes

I've never had a "smart" phone before but have just begun considering getting one. I see data plans talking about how many MB or GB you get per month for a given price. But I have no idea how many bytes are transferred at a time by any of the routine things people do with these gadgets. How many do you upload/download in a typical half-hour on the internet? (Is uploading even included in the total?) How many does it take to look up a local business in a phonebook app or check out what's near you in a map app? How many do the FaceBook app (which I know is different from going to the website in the web browser) or other off-internet apps & games use?

via JREF Forum http://forums.randi.org/showthread.php?t=263205&goto=newpost