Using Blu-Fi messenger you can send messages for free using Wi-Fi and Bluetooth .
People outside Bluetooth range of 15 metres can also receive messages by multi hop routing
You can send message to whole class by sending it to just one student.
Send message to one member of group and transmit it to the whole group
PC client available at : https://rapidshare.com/files/868141518/BluFi_Client.jar
Server can be downloaded from : https://rapidshare.com/files/1460540056/BluFi_Server.jar
Based on the Breadth First Search based multi hop message traversal !!!