The cutthroat competition that pervades today’s smartphone market just got a little more intense. T-Mobile US Inc. (TMUS), the fourth-largest mobile operator in the United States, just announced that its Q1 2014 revenues rose by 47 percent to $6.88 billion. The revenue jump was powered by discounts and promotions that ultimately accounted for TMUS adding 2.4 million new customers in the three months ending March 31, 2014. You can bet Verizon (VZ) and AT&T (T) took notice of TMUS’ 300 percent-plus increase in subscribers over its first quarter 2013 figures. So will investors.