Why does my iphone 4s use cellular data when making a phone call?

If you have a data limit which apparently you have and are concerned about, the ability the turn Cellular Data off is an important option and doesn't change the point of a smartphone.

Have you contacted AT&T technical support regarding this to determine what AT&T may have to do with this?

If no apps are installed, you did not restore from the backup, not using iCloud, not using iMessage, not exchanging MMS, not sure what this would be besides something by AT&T.

When your iPhone is connected to an available wi-fi network, unless your iPhone remains connected to a power source the wi-fi connection will be dropped when the iPhone is locked and not being used.

How could it be an iPhone thing if no apps are installed, you did not restore from the backup, not using iCloud, not using iMessage, and not exchanging MMS?

Sounds like you have tried everything besides call AT&T, so you might was well rule AT&T in or out since you claim nothing whatsoever is being used that could use cellular data.

I understand if the phone is locked and was on wifi that it will lose its wifi connection and use cellular data but what is being transmitted when the phone is locked, especially if everything is shut off.

You are not accessing any email accounts with the Mail app, never exchange iMessage or MMS, never access the Maps app, never launch Safari or any app that requires internet access?

Define "everything is shut off."

Just because you did not launch something like Mail, Mssages, etc, doesn't mean they are not checking with the servers, or servers checking ith the apps. Same for many other apps and services, including the built-in ones that you can't delete.

I will contact AT&T but doesnt the phone control and count how data is being used and then sent to AT&T for reporting?

No way. The data counter on the iPhone is not 100% accurate - what your carrier counts determines your usage which is not based on what the iPhone counts and the same with any cell phone.

Could it be the SIM, even though I have gotten it replaced?

No.

Hogwash. Acknowledged by ATT - what a joke.

Unless you are syncing notes over the air with an account that supports this, opening notes does not use data. If you are syncing notes over the air, launching notes will use a small amount of data.

My iPhone 4S does not use data when I place or receive calls.

Wrong.

If you are syncing notes over the air Einstein, a small amount of data will be used when opening notes - checking if any new notes are available at the server to download. This is by design and intention - hence syncing over the air and only an issue for the brain dead.

If this is what you believe, get rid of it so you can take your clueless habitual whining elsewhere.

are you sure

settings->general->about->diagnostics and usage->"don't send" is turned off?

Surely if you have it connected to WiFi it should route your data through that. I wonder if it just doesn't differentiate between data sent through WiFi and over the air. In that case just keep a track of your data usage through your AT&T account and see if it mirrors your iPhone data report.

Keep us posted because I think that the same issue is happening to mine and thus always going over my data allowance with Vodafone in the UK. I know O2 played this underhand trick when WiFi was first available to phones, even though handsets were connected to WiFi they were charging for data usage

I second the question posed by Rysz....if you have ANYTHING set up at all (a mail account, etc) it will communicate with it's server..whether polling for new mail, syncing notes, etc.

Also, the 4S is designed to be PC Free, so check your General settings tab to make sure it's not checking for Software Updates. Also, are you backing up to iCloud? This will automatically do things in the background. Check the iCloud settings page.

And to ensure no apps are running, double click your home button. When the screen raises up it will show icons of any running apps. Hold your finger on one of them, and they will start to dance with X's on the corners. Tapping the X's closes the app. Close them all, then hold your home button and power button at the same time. Slide to power off, leave it off for a minute, then power back on. This will ensure no apps are running in the background.