If you are reading this, you probably faced a situation similar to mine. You noticed that you were reaching your data limit on your cell phone plan with AT&T and you wanted a way to disable the feature that is causing your data plan to be used on your iPhone.
When you went to Settings > General > Network, you found 2 On/Off switches for 3G and Cellular data. You don’t know which one to disable and what the impact of disabling either will be. Short answer, by simply disabling Cellular Data you will not use anymore of your data plan. You can leave 3G on or off, that is optional. For more info, continue reading, otherwise, GO TURN IT OFF NOW, until your next data usage cycles renews. =)
Okay, if you are interested in knowing a little more or where I received my information, here it is. 3G is a supplemental technology that enables you to talk and surf the web at the same time. It enables faster loading of pages, mail messages, etcetera. So, if you were to disable 3G alone, you are still able to use up your cell phone data. 3G only makes things faster for you.
You are probably wondering: “Will text messaging still work if I disable my Cellular Data?”
The answer is “YES”. They will. In fact, I just finished checking that before I completed this sentence.
If you are the untrusting type, then your next thought may be “How do you know all this?” I got off the phone not more than 5 minutes ago with an AT&T rep and asked the exact same questions.
Thhhaaaaaankks
you helped alottt 
<3 xxxxx
I just got the iphone 3G, 2 weeks ago and started realized today that I was using data even though I thought I was on my home wifi. After I searched the att site, and a few other places, I realize I’m not the only one that has had this problem. I found some great info but you were the only one that answered my question about what the difference is between cellular data and 3G. Thanks for taking the time to share what you learned!
This is useful tips! Thanks! I normally keep my wifi on so my iPhone can detect it wherever I go. If I don’t see it that means it’s time to turn on Cellular Data and if I want it to run faster I turn on 3G as well. 3G will use up battery in the speed of light though. Mind. -_-
I’ve encountered a data usage problem in that I have burned thru my data plan and over incurring an overage charge in less than 5 days into the new billing period. I’m hoping you can assist? I’ve own ed an iPhone 4 about 1.5 yrs, I have a WIFI connection at home where I use the data features the most. I subscribe to the smallest dataplan AT&T offers never utilizing the plan fully during the previous months. I want a data plan in the event I need it when I’m not home. I’ve contacted AT&T they said to go to Apple, Apple said I would have to pay for technical assistance? I don’t understand how this happening I’m at home, I received the text message 3 days into the new billing period that i had used 65% of the plan. I can see the WIFI icon and verified that i am connected, i have a laptop that is working fine off the wireless router. Howeve, I’m still using AT&T’s data plan, the manual states the phone will automatically connect to the previos WIFI connect before going to the carrier’s data plan if you cannot connect to WIFI. The phone is not sending the notification “unable to connect to WIFI”. I’ve turned off the celluar data a few minutes ago but I would like to have Internet access when I am not home. Moreover, i need to find out why all of a sudden my data usage is not running on the WIFI connect when the phone shows it to be?
The undetected usage may be coming from apps that you’ve allowed permission to connect to the internet. For example the facebook app, or more commonly your e-mail account(s). If various apps on your phone have a persistent connection they will be sending and receiving packets of data all the time (even when your phone is not in use). Disable these apps from doing this. Also change your e-mail settings to only download when you open up your e-mail client. That way you have more control of when your data is being used. This may mean that you won’t receive instant facebook updates though, but you can begin enabling certain apps that aren’t data hogs over time (play it by ear).
Also, data usage charts/graphs are not always up to date when you log into your AT&T account, so don’t be surprised if they don’t accurately represent your usage at the moment. My experience is that they are usually a day behind in reflecting your actual data usage.
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Oscar… riddle me this; Am I correct in thinking my safest bet whilst overseas is to simply switch 3g & Cellular data to OFF, thereby disabling any connection whatever between my handset and my phone company?
And so then being reliant on wifi and nothing else?
Or is there a ihole in my itheory?
To answer your question you can simply turn your Cellular data Off (on your iPhone). You don’t need to tinker with the 3G part. That’s optional. But you might as well. You will still be able to send text messages after you do this. That might change when you are overseas though. Check w/ your phone company.
Off topic; When I was in Mexico, I sent a text or two out successfully but did not receive anything back, and I did not have any features disabled. I also made calls (oddly enough the call quality was rather good). I was charged roaming fees for the calls.