LevelUp keeps on keeping on. The not-so-little-anymore Boston-based mobile payments startup announced it now has 1 million registered users.

One million users ditching plastic for their phones may not have card giants like MasterCard and Visa losing any sleep just yet, but the speed with which the company is now adding members is impressive. The company took more than 18 months to reach 500,000 users. Now, just four months after hitting that milestone, LevelUp is at 1 million users.

But sheer numbers have never been LevelUp's goal, something the company has been pretty upfront about since launching in July 2011. Instead, it wants to do something much bigger: revolutionize payments.

And company CEO Seth Priebatsch said LevelUp is putting the finishing touches on its next step in reaching that goal. LevelUp is finalizing the company's API and white-label software development kit so that developers and merchants can easily integrate it into their solutions, turning LevelUp from a payment method to a payment platform, he said.

"We're trying to revolutionize the way people pay," Priebatsch said in a company statement. "But to do that, we need everyone in the payments space to be able to innovate with us and help propel the moment forward."

What the platform play means

The practical effect of LevelUp's platform strategy is to give all the necessary stakeholders in the payment value chain a place to "plug in" to LevelUp tools. For instance, merchants can offer a branded mobile payment app built on LevelUp's core platform or app developers can integrate LevelUp into their own apps offering payments or loyalty or discounts.

After 18 months of putting out a steady stream of news releases, LevelUp's announcement of its platform plans isn't the most surprising news ever. The company has been moving in that direction. It began integrating with major point-of-sale solutions last year. Partners include big names in restaurant point of sale like MICROS, POSitouch and Dineware, which together own 30 percent of the restaurant market.

Merchants who use POS solutions from LevelUp partners can easily accept LevelUp's QR-based, "zero interchange" mobile payment application as a payment method. Along with letting users pay with their phones, the merchants pay no processing and interchange fees on those purchases.

LevelUp also began offering a white-label merchant solution, giving retailers and restaurants the ability to build their own branded-app using LevelUp's technology to make it work. The first restaurant to use the solution, a Washington D.C.-based chain called Sweetgreens, released their app last month.

"Would Facebook have transformed the way we socialize without an open API? No," said Priebatsch. "Would Apple have transformed the way we use mobile devices if only they could build apps? Definitely not! So, as we're trying to push forward the mobile payments revolution, we've decided to make LevelUp into an app store at the payments layer... like what Facebook did at the social layer."

No official word on when the final steps to the LevelUp payment platform will be completed, but one thing is ] sure: LevelUp won't be shy in getting the word out.