How to switch 3G/4G on AT&T HTC One X (Rogers) or Samsung Galaxy S3?

Unfortunately, At&t disabled the 4G/4G LTE switch function which is available on other versions. While, 4G LTE is not always the best choose. Some people want to switch to 3G to save energy. Here is way to do it and I tried on my HTC One X. It works:
go to Settings>Mobile Network>Access Point Names
Click the Menu button, and select "New APN"
Enter the following:
Name: Media Net (name doesn't really matter, as long as its different from the original APN)
APN: wap.cingular
Proxy: Not set
Port: Not set
Username: WAP@CINGULAR.COMPassword: Not set
Server: Not set
MMSC: http://mmsc.cingular.comMMS proxy:
MMS Port: 80
MMS Protocol: WAP 2.0
MCC: 310
MNC: 410
Authentication type: Not set
APN type: default,supl,mms (no spaces after each comma)
Bearer: Unspecified
After entering the values, hit Menu again, and select "Save". Now go back, and you should see your "new" APN listed along with the "original" one (should be AT&T PTA). Just select the new APN, and hit back or home. You will see the 4G LTE icon disappear, and you will lose data for a minute or so (if you use the browser, it will give a no connection error). Then you should see the "4G" icon come up (no LTE), and you should have your data connection back.
original link: