T-Mobile USA, the final member of the wireless Big 4, finally posted second-quarter numbers today.

Let’s recap: Verizon Wireless- 1.5 million new subscribers, for a total of 68.7 million.
AT&T – 1.3 million new subscribers, for a total of 72.9 million.
T-Mobile – 668,000 new subscribers, for a total of 31.5 million.

So at a time that its rivals added some 3.47 million subscribers, Sprint Nextel lost 901,000. For now the company has 51.9 million subscribers, but executives said to expect more losses in the third quarter.

At the time Gary Forsee and Tim Donahue cooked up the Sprint Nextel merger, they said scale matters. Competing at the top of the industry requires big budgets for big marketing campaigns and the heft to receive the hottest handsets from manufacturers.

To be sure, Sprint remains solidly in the industry’s No. 3 position. While Dan Hesse works to stabilize the business, however, the company is slipping.

So does Sprint have a magic number when it comes to subscribers? Would it be significant in terms of its ability to obtain the best handset selection if Sprint
slipped below 50 million subscribers?

Hesse said yesterday that his current focus is on obtaining high-quality customers. He is less worried about matching the overall subscriber growth rates of the top companies in the industry.

Verizon executives seem to think scale still matters. They are preparing to snatch up Alltel and claim the industry’s top spot.

Qwest Communications new deal with Verizon probably will mean the defection of many, if not all, of the 800,000 subscribers Sprint now counts in its tally.

And what would happen if Sprint really did ditch the Nextel part of its business? That network has been hemorrhaging customers, but it still serves about 14.6 million.

Should these events come to pass, Sprint could the gap between itself and T-Mobile shrinking dramatically in the coming quarters.