Square, PayPal, Intuit, Verifone -- the mobile payments field (and we're not talking wallets here) is seriously crowded already. So, the question is then, why on Earth would Groupon want to join the fray? We're not entirely sure, but VentureBeat is reporting the coupon service is preparing to do just that. According to a source within the company, Groupon is testing card-reading dongle and payment platform with surprisingly aggressive pricing. According to the insider, transaction fees will be 1.8 percent, on top of a $0.15 base charge. By comparison, square charges a flat 2.75 percent. Interestingly, the source also claims that Groupon is handing out, not just free readers, but free iPod touches to plug them into. The move makes obvious sense since the company snatched up Kima Labs, makers of TapBuy, in February. Besides, it could easily integrate its discount offers with the platform as a value added service. None of this is confirmed just yet but, we certainly wont be surprised if this rumor pans out.