then determine whether a tdd is connected to the tdd interface 44 step 104 this may be accomplished in two ways the hearing impaired visitor may have been provided a special access code to enter into the keypad k alternatively the processing unit can automatically detect the presence of a tdd at the tdd interface 44 since a tdd operates in a manner similar to a computer modem this detection process is simple and well known the processing unit 30 will then determine the hearing status of the tenant i e whether the tenant is hearing impaired step 106 this is done by accessing the memory subsystem 36 for data corresponding to the desired tenant selected above at step 102 such status information will have been stored within the memory subsystem 36 along with tenant names telephone numbers and other information for use by the present system after it has been determined whether either the visitor or the tenant are hearing impaired or both step 108 a communication link is established between the entry control panel p and the tenant if neither the visitor nor the tenant use a tdd or if both do the tenant is dialed directly step 114 using a telephone number retrieved from the memory subsystem 36 no intermediate steps are required to be performed by the present system if either the tenant or the visitor uses a tdd but not both a relay service is dialed by the entry control panel p step 110 the telephone number for the relay service is programmed and stored within the memory subsystem 36 the relay service is then instructed to.