Smartphones, the migration to Long Term Evolution (LTE) and growth in machine-to-machine (M2M) connections highlighted the seasonably soft second quarter for the wireless operators in the U.S.

While most of their competitors lost contract customers in the quarter, the big two -- Verizon Wireless and AT&T Inc. (NYSE: T) -- continued to get bigger. AT&T sold 3.6 million iPhones in the three months ending in June compared to Verizon iPhone sales of 2.3 million. But Apple Inc. (Nasdaq: AAPL)'s device was just one part of the smartphone story. The advanced devices now make up 36 percent of Verizon's subscriber base and 49.9 percent of AT&T's, as well as growing proportions at their smaller competitors. (See OS Watch: AT&T Outsmarts Verizon in Phones.)

One bragging right Verizon does have over AT&T, however, is 4G. The carrier added 1.2 million new LTE subscribers in the quarter before AT&T has even turned up its LTE network. Sprint Corp. (NYSE: S) also bet on the 4G variation to WiMax, announcing a spectrum hosting deal with LightSquared and causing Sprint WiMax partner Clearwire LLC (Nasdaq: CLWR) to look at moving to Long Term Evolution Time Division Duplex (LTE TDD) on its own. (See Sprint, LightSquared Strike Agreement and Clearwire Goes It Alone With Faster 4G.)

While 3G and 4G growth brought in the most ARPU [average revenue per user] for the wireless operators, it was actually non-voice-based subscriptions that had the most growth in the second quarter. More non-operator branded M2M subscriptions were added than voice subscribers at AT&T, Verizon, Sprint Corp. (NYSE: S) and T-Mobile US Inc. , representing the next wave of growth in wireless.

Here's a look at how the top eight operators in the U.S. fared on some other key metrics for the second quarter:

Table 1: Tier 1 Wireless Operators Q2 Scorecard

Table 2: Tier 2 Wireless Operators Q2 Scorecard

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— Sarah Reedy, Senior Reporter, Light Reading Mobile