It's not every day that the U.S. government files a lawsuit against an Apple iPhone. I noticed the lawsuit over the weekend and started looking into it, thinking at first that the government might be taking action against Apple's decision to offer the iPhone exclusively through AT&T.

A quick glance at the legal filing information, however, makes it clear the case is nothing of the sort. The U.S. Attorney in Chicago has filed for a warrant to search a specific Apple iPhone, presumably because the phone contains data related to a government investigation.

A call to the press duty officer at the U.S. Department of Justice on Sunday wasn't returned, but speaking to a clerk in the office of Illinois Northern District Court Judge Susan E. Cox on Monday, I learned that the case was under seal and thus legal filings would not be made available online or off.

The press officer at the U.S. Attorney's Office in Chicago said she could not provide any information about the case.

The phone number of the iPhone is listed in what little legal information about the case can be found online. It's not an AT&T number, as one might expect. Rather, a reverse phone lookup suggests that it's a T-Mobile number. So presumably someone hacked the iPhone in question to run on T-Mobile's network.

A call to the number resulted in someone hanging up.

Three individuals with Chicago addresses are associated with the phone number in question, according to an Intellius phone number search. Could this be an identity theft investigation? Or an attempt to make a cybercrime case against an iPhone hacker?

Perhaps in time further information will come to light. At the moment, it's not clear why the government wants to inspect this particular iPhone.