The US-based National Investor Relations Institute (NIRI) says that 92% of companies represented by their members conduct earnings calls and that virtually all of these are webcast.
The calls are usually preceded or accompanied by a press release containing a summary of the financial results, and possibly by a more detailed filing under securities law.
Depending on the size and complexity of the company, the difference between actual and expected results, and other factors, the length of the call will vary.
However, keeping the investor and analyst communities happy is part of management's job, so the call will generally be announced a few days or weeks in advance.
Some companies with shares publicly listed also have American Depositary Receipts (ADRs) that are traded on US stock exchanges and are required to file Forms 20-F and 6K with the SEC.