Off-topic: How do people typically go over 3GB in a month? The only time I came close was when Spotify forced a re-download of all my previously-cached music and I had my wifi turned off. My IT person (in a company <50) said I'm the only person to have ever gone near 2GB.
I'm sure you can easily go over the limit by streaming Netflix...but I generally watch Netflix at home.
My billing cycle ends tomorrow and I'm at 5935.74 MB. For me it's streaming podcasts (managing downloads in iTunes is a pain), YouTube, and lots of web browsing. During the MLB season I probably use even more, because I stream multiple games per day (I haven't checked this). I also semi-frequently buy albums from iTunes on the phone.
In short, it's not very hard if you use the phone like I do.
Edit: Wow, it actually appears I was hovering around 1GB per month until last September, during which I used 2.7GB -- a jump from 0.5 GB the month before -- and after which it's been a close-to-linear increase. Weird. I didn't realize my habits have so drastically changed.
On my Android phone I use the doggcatcher app to download podcasts. I go well over 3gb each month, but as a Sprint customer I currently do not need to worry about the limits.
I could certainly set the app to only download on wifi and avoid the issue entirely. However, it is quite nice to have it check hourly for new podcasts and download them at that point no matter where I am.
AT&T has pushed on us hard. We pay almost $200 for 2 people. We will be moving over to T-Mobile when the contract is up. It will save us almost $100 a month and still keep the unlimited plan. Ive had enough of AT&T for a while, im just waiting for this damn contract to be done with.
You probably do it trivially on your land line, no? Synchronize a big dropbox share, upload all your music to Google Music, etc...
Now picture if you were poor (edit: first world hipster poor, anyway), and had to decide between the wired broadband and a smart phone that was almost as fast.
I used to push very near, or even exceed 2GB when I was listening to Pandora/LastFM/GrooveShark all the time. I hate commercials, so I used my phone as a radio playing device when I was in my car, and I was in my car a lot. I also occassionally look up YouTube videos, connect to my server via SSH and a variety of other things.
I'm sure you can easily go over the limit by streaming Netflix...but I generally watch Netflix at home.