We consider a complete graph of n nodes, any pair of which can communicate with each other directly through one of F available wireless channels. n is not known to the nodes. Time is divided into synchronous rounds. In each round, a node can select at most one channel to listen to or transmit on. Transmission is successful if there is exactly one node transmitting on a channel (and one or more nodes listening). If two or more nodes transmit on the same channel, a collision occurs and their transmissions fail. Nodes can detect collisions, i.e., can distinguish collision from silence. We study distributed solutions to the information exchange problem: given initially k nodes each holding a packet, the task is to disseminate these k packets to all n nodes as quickly as possible.