way subscribers are reminded that messages are waiting at the central station of course the messages need not be retrieved at this time however the subscribers are reminded that messages are available for review following the transition in step 204 or upon a negative determination of decision 202 the routine proceeds to decision 206 which determines whether a channel is available on the communication system 100 if not a 34 no channel available 34 message is sent step 208 and the routine proceeds to reference letter c of fig2 b if there are channels available the routine proceeds to decision 210 which determines whether the called subscriber is currently participating in another call and is therefore busy and unable to respond to the present call request if the controller 102 determines that the called subscriber is busy the routine proceeds to step 212 which transmits a 34 unit busy 34 message to the calling subscriber prior to routing control to reference letter c of fig2 b however if the called subscriber is not busy the routine proceeds to step 214 where the central station transmits a message 114 containing the identity of the calling subscriber unit optionally the central may send the channel information at this time step 216 which will enable the called.