Sprint halved its capital expenditures between the first and second quarters, reducing investment in not only its primary CDMA and iDEN networks, but cutting spending on its still-fledgling WiMAX network as it waits for its joint venture with Clearwire to close.

Sprint posted a $344 million second-quarter loss today, losing 901,000 net subscribers—most of them valuable postpaid customers—and seeing its total revenue fall 11%. Sprint, however, managed to staunch some of the major bleeding from the quarter before and showed progress in improving its churn rate, but Sprint warned it expected things to get worse again before they get better.

Sprint’s financial misfortunes also appear to be the misfortunes of its major wireless vendors. Last month Nokia Siemens Networks, Alcatel-Lucent and Nortel all reported poor second-quarter results in North America, and both Alcatel-Lucent and Nortel fingered a major CDMA provider’s cut in capex as the culprit. Sprint was never named, but most analysts suspected the suffering No. 3 mobile operator was the likely suspect. Today that speculation was all but confirmed by Sprint chief financial officer Bob Burst when he announced Sprint’s capex for the second quarter fell 61% year-over-year to $646 million, and its total wireless capex for the first half of the year was less than half of that in 2007. Furthermore, Burst said, Sprint expects spending to remain flat for the second half, so vendors shouldn’t expect any big uptake in orders in upcoming quarters.

Sprint accomplished most of its major priorities in 2007, Burst said: upgrading the EV-DO to Revision A, deploying Qualcomm’s QChat push-to-talk technology throughout the CDMA network and expanding the CDMA network to match its Nextel iDEN footprint. But Sprint hasn’t just gone through its network wish list; its shrinking customer base is also responsible for its shift in investment priorities.