Verizon and AT&T are still far and away the wireless market leaders in the United States. The "big four" networks are really comprised of two giants distantly followed by two large carriers. The giants both have grown in the last year, as has Sprint. T-Mobile, on the other hand, is simply treading water.

Verizon has just over 107 million subscribers, growing about 6.6% since last year. Second place AT&T is within grasp of 101 million, a 7.8% increase over last year. Sprint follows in third place with 53.1 million subscribers, and T-Mobile is in fourth with 33.7 million subscribers. That makes 294.8 million subscribers, combined, for all four networks.

To put that in perspective, the population of the United States is 312.6 million. Add the other 30 million or so subscribers on the fifth through tenth place networks and, on average, there is more than one device per person in this country. Granted not every device is a phone. Tablets, e-readers, 3G/4G hotspots, and other devices represent some of those subscribers, but the numbers are impressive nonetheless.

The data accumulated by FierceWireless indicates Verizon's average revenue per user (ARPU) is $53.21, second only to US Cellular's ARPU of $58.09. No other carrier even breaks the $50 mark.

If AT&T and T-Mobile get together, combined subscribers will approach 134 million, well ahead of Verizon. Revenue for the combined entity would approach $20 billion dollars.

Something the top two carriers have in common is industry-leading low churn rates, which are around 1.25%. Sprint's is more than double that at 2.56%, and T-Mobile has nearly three times more at 3.5%. The two giants also get roughly 40% of their revenue from data charges. Sprint's number wasn't available, but T-Mobile's was considerably lower at 30%.

Numbers don't tell the whole story of course, but when you look at ARPU, churn rates, and data penetration, size appears to matter. It only goes to highlight the issues Sprint will face if the AT&T/T-Mobile merger is approved. I tend to think momentum would continue to push Verizon and AT&T/T-Mobile further up until a duopoly is created, while Sprint drifts down until it is no longer recognized as a major national player.