Just now i tested an iphone using the ComfortDelgro Booking app .
Iphone IOS6 actually set permanently the caller number into the app . As in first time usage , the number will be permanent .
No other number can be edited . Unless u uninstal the app and reinstal it , maybe can key in another number .
But that still cannot stop the pranks .... one kaki kena an Advance Booking ( Mercedes Advance $18) , he smart , after hearing my stories , he quickly dial in to confirm with pax ..... the number he called , was diverted to a Thailand Int'l Number .
He called in to cancell after filing a complaint for such pranks .