According to Newtons Telecom Dictionary, this is a shortened but perfectly acceptable way of saying telecommunications, which has replaced the word "telephony" in common usage. It's easier to say than anything equivalent and covers datacom. It has a broader definition than telephony, which the general public thinks means voice communications over a telephone. Any dictionary will tell you that telephony only covers speech. Use telecom.

The shortened form most Australians use when referring to Telecom Australia. Mostly privatised by the Australian Government to raise capital and called Telstra these days, a small part of the former giant remains.