If you click on products, you will see an alert service...you didn't mention free or not..this one isn't....I found it by googling earnings announcement.. http://www.wallstreethorizon.com/index.asp
during earning season there plenty of days,where number of reporting companies will be more than hundred. you really need your own program or whatever to filter all those small cap,low volume, pre\after market etc. i mean-email alert service maybe ok, but-still too much work after you got it.