Advertisers pay 10c per user to get their wallpaper on a smartphone screen for 24 hours, which David says is actually very cheap given that many people look at their devices around a hundred and fifty times each day.
Little Lot is also a "zero-cost funding raising platform" for charities, which don't have to put any money towards the service to get something back from it, he said.
The startup says it aims to take advantage of "slacktivism", the growing practice of people supporting charities or organisations on social media but not actually donating money towards a cause.
"Slacktivism comes up all the time and it's really relevant to us because we're tapping into that idealistic energy to do something to try to right the world," Stephen said.
While the public may want to make change, Stephen said people aren't reaching into their pockets and contributing towards causes they believe in.
"I think what we've actually done is find a cool way to convert that energy, that slacktivism, into real money for the charities," he said.
The name Little Lot, David said, stemmed from the idea that if enough people contribute a little, it adds up to a lot for the organisations receiving the funds.
Asked if the startup was a charity or a business, Stephen said it was a "social enterprise" which had both philanthropic and profitable motives.
The reality was that if Little Lot ran as a not-for-profit, it wouldn't be able to raise the capital it needed to expand, he said.
The company, which is privately-funded, still takes a 25 per cent cut of the platform's ad revenue.
"No matter how much money we happen to make, charities would have made three times as much. You can't say that's not a good outcome," David said.
The brothers already have experience using the Little Lot model with their existing venture, Donate your Desktop. This involves advertisers renting out a user's computer screen desktop, with funds going to charity.
The pair plan to migrate 2500 active users from Donate Your Desktop on to Little Lot and hope to have 20,000 users by the end of January next year.
Advertisers already using Little Lot include House of Travel, Barfoot & Thompson, Sitka and Bivouac.
The system is currently only available on Android-based smartphones.
Check out their Facebook page here.