By Slash Lane

Published: 03:50 PM EST (12:50 PM PST)

Just three days before Apple officially unveiled iPhone 4, the company requested that the Federal Communications Commission keep photos and information of the handset secret for 45 days.

The letter obtained and published by Patently Apple, was addressed to the FCC and signed by Robert Steinfeld, EMC and wireless compliance manager with Apple. It cites a desire to keep information about the inner workings of the iPhone secret, despite the fact that the phone was set to be publicly unveiled, and prototypes were disassembled well before that.

"Although Apple has begun to market the device publicly, these documents reveal technical and design information that has not yet been publicly disclosed in such marketing and that is protected by Apple as confidential and proprietary secrets," the letter reads.

It requests a 45-day short-term confidentiality agreement for photographs related to test setup, external, and internal views of the hardware, as well as the user manual. Apple has also asked for permanent confidentiality related to a number of specifics, including schematics and bills of material for the cellular radio, Wi-Fi and Bluetooth functionality.

It is standard practice for Apple to request confidentiality from the FCC. But the request has been viewed as curious by some, considering that prototypes of the near-final iPhone 4 design were publicly disassembled, revealing many of the new device's secrets.

One secret that Apple managed to keep under wraps until last week was the amount of RAM within its latest iPhone. While reports had suggested the A4 had 256MB of embedded RAM -- the same amount found inside the iPad -- Apple reportedly disclosed to developers during last week's Worldwide Developers Conference that the handset actually features 512MB of RAM, doubling that of last year's iPhone 3GS.

Other technical details and features that Apple might want to keep secret could include secrets such as:

• The design and features of its A4 SoC, which is significantly different from other SoCs sharing its same Cortex A8 CPU core.
  
• Details related to the performance of iPhone 4's new stainless steel frame antenna.
  
• Likely new cellular radio support for pentaband UMTS I,II,V,VI,VIII (850/900/1700/1900/2100MHz) 3G bands, enabling improved reception for markets like Japan and New Zealand that use the UMTS 800MHz band VI. Current iPhones (and other smartphones) typically offer quadband UMTS. Apple is currently advertising quadband support, but FCC filings indicate that iPhone 4 is actually a pentaband phone.
  
• Possible cellular radio support for the AWS UMTS IV band (advanced wireless spectrum), enabling compatibility with the 3G UMTS service T-Mobile operates in the US.
  
• Possible cellular radio support for CDMA/EVDO, enabling the rumored hybrid operation on Verizon and Sprint.