A method of and system to determine which channels are accessible by a communication device in a push-to-talk communication network are disclosed. The method may comprise sending an identifying network connectivity message to the communication device across a particular network channel, the identifying network connectivity message including an identification code. The method further comprises querying the communication device for the identification code to determine if the communication device successfully received the identifying network connectivity message, thereby to establish if the particular network channel is accessible by the communication device.