Groupon is throwing its hat in the mobile payments ring, announcing today its launch of Groupon Payments — a service that will allow merchants to process credit card payments from customers using an iPhone or iPod Touch. If that sounds a lot like what Square is doing, that's because it is: Groupon Payments will hook merchants up with a similar card-swiping dongle, and the company says it offers the "lowest rates" for transactions.

While the mobile payments business is currently crowded by several companies that all want a piece of the future, Groupon could get a head-start from its existing relationships with merchants. The company says that participating businesses will be able to use the app to scan and redeem Groupons, which could be an attractive tie-in for those who already give Groupon discounts to customers. We'll have to wait see if yet-another mobile payment system can take hold -- as it stands, Groupon has some catching up to do.