Slidejoy offers users cash for ad space on their lock screen.A square inch on a smartphone homescreens is perhaps some of the most valuable advertising real estate available. A company called Slidejoy hopes to make that real estate a little more accessible to brands. 

Slidejoy, which recently launched on Android, offers users money for allowing brands to advertise on their phone's lock screen. 

It works very much the way Amazon's Kindle with Ads works. Every time a user goes to unlock their phone, they'll see an advertisement. The user can then either swipe left to interact with that brand or right to proceed to their phone's homescreen. Slidejoy will keep track of which ads a given user interacts with and tailor impressions to their tastes. In return for installing the app on their phone, end users can earn anywhere from $5 to $15 per month, and it doesn't matter whether you swipe left or right.  

"Either way, it's the exact same amount of money, and there's no set amount per ad that you're watching," said Robert Seo, the company's CEO. 

The company is already serving ads from some big names like Macy's, Adidas, and Groupon among many others. Seo said Slidejoy is currently working with ad networks that couldn't be named at this time. 

Slidejoy's said it would love to work directly with the carriers, possibly getting deep integration with their billing systems so end users could earn money directly off their wireless bills. 

"Obviously, we could provide a huge amount of value to carriers," Seo said. 

For now, Slidejoy users can cash out what they've earned for using the service or donate that money to a charity of their choice.