They do not receive call backs having only an "out of service" response. Obviously they don't want to be up front so bye-bye ... "BLOCK"!
Area code 905 (with overlay area codes 289 and 365) is a telephone dialing area in southern Ontario, Canada, 289-434-xxxx specifically in the Oshawa/St Catherines districts.
The incumbent local exchange carrier for these area codes is Bell Canada