Target, Walmart, Lowe's, 7-11, Best Buy, a whole bunch of big retailers are teaming up on a new mobile payment system. It's called Merchant Customer Exchange or MCX and it will let you pay for things using your smartphone. They're not the only ones trying this. Google has the Google Wallet system. AT&T, Verizon and T-Mobile are planning to launch one soon as well. So why is everyone racing to join in? It's all about being most popular, and eventually getting the most data from you.