Not mentioned in the spectacular quarterly sales results Apple released Monday was a stunning fact: Nearly 18 percent of iPhones sold in the past four months can't be accounted for.

Out of 1.4 million iPhones sold since the hot gadget debuted June 29, fully 250,000 have not been activated to run on AT&T's wireless network, The New York Times and The Register, a British technology blog, both reported Tuesday.

An Apple executive admitted the discrepancy during a conference call with analysts following the release of fourth-quarter performance results.

"[A] number of [iPhones] were sold to people that have an intention to unlock and where we don't know precisely how many people are doing that, our current guess is there is probably 250,000 of the 1.4 million that we sold where people had bought them with the intention of doing that," said Chief Operating Officer Timothy B. Cook. "Many of those happened after the [September] price cut."

• Click here to read a full transcript of the conference call.

AT&T has a multiyear exclusive deal to carry the iPhone's signal in the U.S., and each unit is "locked" to work only with AT&T.

Several hackers popped up in late August claiming to have "unlocked" the iPhone so it would run on different networks, but Apple quashed many of those workarounds with a software update last month.

Demand for iPhones is high overseas, but they won't go on sale in Britain and Germany until next month.

In France, Apple is being forced to sell a higher-priced factory-unlocked model alongside its locked version to comply with local law.

No announcements have been made regarding iPhone availability in any other countries.

• Click here to read the Register story, and here to read the New York Times story.