Here’s a quick overview of the the hardware technical specifications, software and OS features and FAQs for Apple iPhone.

Processor: XScale from Marvell Technology Group. Update: Engadget reports the iPhone features a 620MHz ARM1176JZF chip with TrustZone & Jazelle (hardware acceleration engine for Java)
Storage capacity: 4GB/8GB flash drive
Operating System: Mac OS X Mobile
Screen Size: 320 x 480 pixels at 160 ppi, 3.5 inches colour screen;
Band: GSM Quad-band (850, 900, 1800, 1900 MHz)
Wireless: Wi-Fi (802.11b/g), EDGE and Bluetooth 2.0+EDR
Camera: 2.0 Megapixel; 1600 x 1200 pixels
Input, Navigation & Interface: Touch Screen architecture(recognizes finger gestures with up to four fingers at once), sliding interface with 360° view, portrait & landscape modes, Accelerometer sensor for auto-rotate, Proximity sensor for auto turn-off;
Audio: AAC, MP3 VBR, Apple Lossless, AIFF, and WAV
Video: H.264 video (640 X 480 pixels, 30 fps), stereo audio in .m4v, .mp4, and .mov file formats, MPEG4 (640 X 480 pixels, 30 fps)
Battery: Built-in rechargeable lithium ion battery
Headset: Wireless Bluetooth Headsets (Apple iPhone Bluetooth Headset or any other such as Motorola, jabra) & wired Stereo earphones with built-in microphone
Accessories: Any hardware that supports 30-pin dock connector such as iPod. Should have a “Works with iPhone” logo.
System Requirements: Mac OSX, Windows XP and Windows Vista with USB 2.0 with iTunes 7.3
Security: VPN and WiFi WEP/WPA
Email: HTML email client, IMAP, POP3, Exchange Activesync Direct Push and webmail such as Yahoo! Mail, Google Gmail, AOL, and .Mac Mail. Multiple accounts can be configured
Attachments: Picture attachments (JPEG, GIF, and TIFF) as well as PDF, Microsoft Word, and Microsoft Excel email attachments
Synchronization: Bookmarks from PC/Mac browser, Music from iTunes for PC/Mac & Contacts and calendar with Microsoft Outlook on a Windows PC, Address Book/Entourage on a Mac or or Internet service, Photos from iPhoto (Mac) or Photoshop (Windows) or any other folder.
Activation: Through iTunes 7.3
Applications and softwares: Web browser (Safari) based Web 2.0 applications/widgets, a list of which can be found here and here
Update: User Guide (9.6MB)

If you have something to add, do let me know!