Update: Turns out the app is out already. AT&T Enhanced Push-To-Talk
AT&T has announced that they would soon launch a push-to-talk service on their network for owners of Apple iPhone 4S and iPhone 5.
The company said that the service would support up to 1000 contacts and group calling with up to 250 people.
Push-to-talk was a popular feature offered by Nextel which is now owned by Sprint. Incidentally, there are a bunch of smartphone apps that offer a similar functionality but they require a data connection.
AT&T’s service is also likely to work through an app. It is not clear if it would work on cellular connections or would need data as well.