Group Chat Messenger is the first application to make direct phone to phone communication possible using PUSH notifications.
You can create your own chat channels/groups and communicate with your friend in the same channel.
The application can be closed, when there is activity in the channel, you'll be notified using Windows Phone 7 PUSH messaging.
Groups are always private (for now), but anybody can join any group if they know the name of the group. Group listing will be available in the future.
The application features a free Trial mode so you can test the functionality.
The application can be found in the "Social" category.
Zune link: http://social.zune.net/redirect?type=phoneApp&id=514c13e2-79f6-df11-9264-00237de2db9e