anallawalla - 9:39 am on Apr 25, 2013 (gmt 0)
This depends on the nature of the company. I know Australian companies e.g. banks who don't give out local numbers to customers, but will show the same 13nnnn number for all of their branches. A 13nnnn or 1300nnnnnn number allows someone to reach their nearest outlet for the price of a local call, e.g. Pizza Hut without needing to look it up. It allows national ads to use just one number.
Might be a special case for Australia. I haven't checked for 1800 numbers, which are freecall.