Sprint Nextel (NYSE: S) has been making progress on its Network Vision thing, but it's had to do it like that daredevil inching his way on a wire strung between the Twin Towers -- plenty of "oohs" and "ahs" below from those waiting on the fatal misstep.

One big Network Vision move Sprint has taken in its journey toward profitability has been in dismantling its unwieldy Nextel iDEN network. But the question for many investors waiting on Sprint's upcoming second-quarter earnings release is just how many of those iDEN subscribers will have stuck with the network.

Analyst Craig Moffett of Sanford C. Bernstein has noted that "How Sprint fares on this critical dimension will be a key metric to watch." Those bullish on Sprint believe "it can return to sustainable growth once iDEN is finally behind it," he wrote in a research note.

The carrier is hoping to keep those iDEN push-to-talk customers by switching them to its new CDMA network Direct Connect service. Last quarter, Sprint was able to keep almost half of those customers leaving the Nextel network. But iDEN is not completely gone. That won't happen until June 2013, according to Sprint.

How do other analysts feel about Sprint's quarterly numbers? Analysts see the company losing $0.40 a share, $0.01 a share better than the loss Sprint incurred for the first quarter. That survey also sees flat sequential revenue at $8.7 billion.

Sprint's most recent move, the better-late-than-never launch of its newest network, finally brings it into the 4G LTE arena where its biggest rivals, AT&T (NYSE: T) and Verizon (NYSE: VZ), have a significant lead. Sprint's debut with 15 LTE markets pales in comparison to Verizon's 330 markets and AT&T's 47.

With the expected launch of the LTE iPhone 5 coming up in the fall, it will be imperative for Sprint to scurry a bit faster if it wants to make it across the abyss.

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