500MB last month on my iPhone with Sprint, which is probably typical. But I'm almost always on WiFi (home, work, client, hotel) and also have an AT&T MiFi device.

Generally I use between 500MB - 1GB a month.

The most I have used is 8.8GB when I moved into my house and was waiting for my broadband connection to be installed. Thankfully my phone provider (Vodafone UK) gave me a 3 month unlimited data test drive for renewing my contract.

You might look at using something like Onovo Extend. It's available (free) on Google Play.
"Onavo Extend lets you get up to five times more out of your data plan without changing the way you use your phone. With Onavo Extend, engage in more app activities, photo sharing, web browsing and more on 3/4G without breaking your data cap. The app lets you compress your mobile data so that you can do more with your Android’s mobile data month after month. And, if you travel abroad, Onavo Extend helps you stay within your roaming plan and saves you money while helping you do more with your data plan."

i used between 4 to 5gb of 4G data as i listen to radios,watch some videos

I have unlimited on ATT with an iphone, but only use about 250-400MB a month. usually the phone is on WIFI at home or work, or sbux or something. I have about seven email accounts, stream with a slingbox, download apps while remote, and do a lot of traffic/navigation stuff. I'm not really sure HOW one gets up to 6GB a month of usage.

Stop using wifi and keep doing the stuff your listed and you may well quickly see HOW.

I use a T-mobile hotspot as my primary internet link. I usually exceed 5GiB per month. Thank God for no overage charges.

Since I got the iPhone 5, I've been using my 4G connection everywhere (with the exception of downloading TV shows/streaming) mainly because it's faster than my home connection and all public hotspots (50Mbps vs 12Mbps)

So in any given month I would exceed my 20gb limit.

We use about 500 MB/month. Both phones are on wifi at home, and hers is also at work. We have an unlimited plan, but it doesn't appear necessary at this time. Downgrading would save us nothing though.

For me varies with travel a bit, but average month with 4-5 business trips and being attentive to use wifi whenever possible. My iPhone and iPad (combined data plan) typically use 4gb or so. Typical use with some music/ radio streaming.

Ended up changing plan and now on the 500MB 4G and unlimited 2G.

Turned on wifi at home and in office. Most usage seemed to be Google Maps, so changed to TomTom, no data required.

Will see how we get on.

My car now has built-in navigation, but I didn't use it all that much on the phone. Maybe 1 or 2 times per month, on average. I don't expect too much of a change in my usage as a result, but that is a factor that I forgot about.

Damn! That is solid value.