After 4 weeks with my iPhone 3G, I thought I would share some of the statistics that the phone has been keeping on my usage:

Songs: 520
Videos: 0
Photos: 18
Capacity: 14.6 GB
Available: 11.8 GB

Call Time
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Call Time: 2hrs and 25mins

Cellular Network Data
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Sent: 3.2 MB
Received: 51.2 MB

Based on these numbers, here are some basic averages (based on 28 days):
5.2 mins of phone conversation a day
0.114 MB data sent a day
1.828 MB data received a day

I have found, that I am using it primarily for reading email and rss feeds (google-reader), and was keeping up with the Olympics news on it as well. I also use the music a fair amount, and I am hoping to find a couple of good podcasts that I can listen to on the commute time (to learn something while I drive :-).