My samsung infuse only connects to the internet when it is connected to wifi, this includes internet based apps. But when I am not connected to wifi, I cannot use the internet or the apps. And I have data network mode activated if that changes anything. Please help.
Did you use your old SIM card or did you activate the new one that came with the phone? My boyfriends phone was having that exact problem, it would work at home when it was connected to our home wi-fi, but it wouldn't work outside of that. The problem was that we just stuck his previous SIM card in the new phone. When we called AT&T and went through the activation process, it fixed the problem.
Correct, part of the so called activation process is migrate your old data plan into 4G data plan. You will need this to use the data connection out of box on any AT&T 4G phone. Don't worry, in most cases, you won't lose your unlimited data.
Some times, even the store clerk sometimes forgets to do this when you purchase phone. You can always call up AT&T and ask them to do so.