Virgin Mobile has become the first Australian telco to let users roll unused data over to the next month.
The feature will be built into new plans from Thursday, while existing customers can get it by upgrading.
"It gives people a second chance to use the data they've paid for," said Virgin Mobile chief David Scribner.
He said about four in five Virgin customers have spare data left over each month, which is essentially forfeited.
"They should get another chance to use it."
Excess data charges from blown monthly allowances have been a growing complaint across the board in recent years.
Consumer groups Choice and the Australian Communications Consumer Action Network have both called for data rollover, which has been pioneered by US telcos AT&T and T-Mobile.
