The U.S. Federal Communications Commission (FCC) has certified the iPhone for use. When Steve Jobs announced the new smartphone at Macworld Expo in January 2007, he said it would take some time to pass the necessary FCC tests (see "iPhone Seeks to Redefine the Mobile Phone," 2007-01-15). With a release that still seems likely in June, Jobs estimated the time frame accurately. Apple filed many testing reports and documents with the FCC in February and March, but a few items have early May dates, indicating re-tests or new tests. Certification is required in advance of offering the phone for sale.
AppleInsider appears to be the first news site to have noticed the FCC filings, which are available in a database when released, but typically are not announced by the agency or manufacturers. Apple later confirmed the timing with Reuters based on this certification.
Because the iPhone handles cellular calls and data, plus Wi-Fi, the FCC certification is in four parts, two for each set of frequencies. The iPhone uses the worldwide GSM standard, which only AT&T and T-Mobile employ in the United States. AT&T's licensed cell frequencies are grouped in two separate ranges. The iPhone also features Wi-Fi for browsing and email - the major two services initially announced by Apple - and Wi-Fi also requires certification. (Verizon uses only one cell standard, called CDMA, which is in widespread use only in South Korea and the United States; Sprint Nextel primarily uses CDMA, and is working to move its Nextel customers from an even less-used standard.)
The iPhone is a quad-band phone, Apple said at launch, but two of the four frequency bands aren't available for use in the United States, and thus not only can they not be used here, but the FCC doesn't need to - cannot really - certify them. Other regulators will issue their own certifications in their own countries for use of those bands.
You can view the filings at the FCC site through its engineering site search engine. The FCC unfortunately fails to provide persistent URLs for searches. At the top of the search engine in the Grantee Code field enter BCG; in the Product Code field enter A1203.
IDG News Service reports that AT&T employees may now take iPhones outside their offices for testing, according to an unnamed AT&T employee. Features on the phone are being lit up one by one, the report says, with music, video playback, and visual voicemail currently disabled - three of four features most in demand from this device, I'd wager! (The fourth? Web browsing.)