Wikipedia
Flagfall or flag fall is a common Australian expression for a fixed start fee, especially in the taxi and haulage and railroad industries. From the Australian mobile phone industry, the expression has recently begun to spread to other English language countries, as business jargon for an initial fixed fee for establishing each phone call. The logic behind is believed to be a method used by Australian mobile phone companies to recover a component of the carriage charges they incur in completing a call to a subscriber being the termination rates, based on the price terms and conditions for the mobile terminating access service (MTAS). The Australian Consumer and Competition Commission is reviewing these arrangements.
The expression is also beginning to find its way into other businesses as a synonym to "start fee". The taxi expression is also being used in Hong Kong, New Zealand, and some other countries, but hasn't been used there as a general synonym for start fee.