Popular deal website Groupon is venturing into the world of smart phone-based credit card payments today, launching the Groupon Payments initiative nationwide after a successful pilot program is the San Francisco Bay Area earlier this year. Groupon's boasting a guaranteed lowest cost pricing to merchants using Groupon Payments for credit card transactions -- MasterCard, Visa, and Discover will cost retailers 1.8 percent of credit card sales, plus a $0.15 per transaction fee, while American Express will cost three percent of credit card sales, plus a $0.15 per transaction fee. The biggest competi
