The first thing you notice about the N900 is its size. It's certainly hefty at 110.9 x 59.8 x 18mm, and the weight of 181g means it's not going to win any slimming contests either. But it's worth pointing out that Nokia hasn't once said that the N900 is a phone, a successor to the N97 or anything along those lines - it sees it as super-charged internet tablet with phone capabilities, rather than the other way around.
The surface of the N900 is a smooth black matte finish. The build material is durable aluminum, steel and rubber/plastic. The N900 easily fits in a pocket, being smaller than the N810 but thicker than an iPhone. The four front components are the status light, proximity sensor, ambient light sensor, and VGA camera. There is a consumer infrared port (universal remote), wrist strap option, stylus and kickstand. The removable back contains the main camera, SIM, battery and microSDHC slot. Removal requires some strength but it's reassuring knowing it won't fall off.
The keyboard is side-sliding with a smooth, springless mechanism, giving it a very solid feel. The keyboard is three-row, localized and backlit with rubberized key surfaces. There is 480i resolution TV-out which uses an included 3.5mm jack with 4 rings. These are ground, audio left and right, and composite video. Useful for watching movies, playing games or doing work that requires a big screen. The 16 million color, 800x480 pixel display is incredible. It is pressure-sensitive, 15:9 aspect and transflective, making the screen easier to see in direct light. It uses a surprisingly responsive resistive touch screen allowing use with gloves, fingernails or a stylus. The ambient light sensor adjusts the brightness automatically.
The main camera is a 5MP Carl Zeiss, the same as the Nokia N97. It comes with a sliding shutter to protect the recessed lens. There is also a front-facing 640x480 webcam. The camera interface is the same as the S60. The image quality is sharp, skin tones are vivid and there is very little, if any, chromatic aberration at the edges. The battery is a 1320mAh Nokia BL-5J, 22% smaller than the BP-4L. A full battery with unoptimized settings allows about 5-9 hours of continuous talk time, 5 hours of music or a few hours of 3G. 3G/3.5G drains the battery faster than Wi-Fi. Lowering brightness, removing desktop widgets and disabling GPS, Wi-Fi, Bluetooth and 3G easily triples battery life. Charging is through microUSB which takes about 4-5 hours for an empty battery.
The N900 has two memory chips. The first is a 32GB eMMC: 768MB of 'virtual memory' (swap), 2GB for settings and software (ext3 /home), the last ~26GB (MyDocs) is for your files only (software not allowed). The second chip is 256MB of NAND memory (RAM) used for bootloader, kernel and rootfs, twice that of the N810. The GPS is a real GPS and has been improved over the N810 due to the addition of assisted GPS. The cold fix time with data is about 10-40 seconds with accuracy as good as the Nokia N97. The builtin FM transmitter transmits the audio from the device into radio frequency so you can tune your car radio to that frequency and play N900 media wirelessly. The signal strength of the N900's 3G radio is weak. It is possible to turn off the cellular radio without disabling Wi-Fi/Bluetooth by going into offline mode and then manually enabling either. Bluetooth DUN and PAN modes are supported via community software. Advanced WLAN security, like different kinds of EAP (EAP-PEAP, EAP-MSCHAPv2, etc.), different ciphers (RSA, 3DES, SHA, etc.) and "authority certificates" (algorithms like X.509, SHA1RSA) are all supported. With Bluetooth DUN, tethering is supported.
The built-in stereo speakers are loud but lacking in bass. They make an acceptable portable radio. Bluetooth headphones work great. The audio quality of the 3.5mm jack is loud and slightly more "forward" sounding than the more "laid back" or "polite" sound of other smartphones but without the response peaks, valleys or ripples that so often mar the critical 1,000 Hz. region. Audio sounds more "present" than with similar devices. The included earphones have a somewhat dirty signal. Higher frequencies hiss, losing details and the brightness and dynamic volume are shallow, lacking weight and depth. The earphone wires feel like they will become loose over time.
People are saying the N900 is not a Nokia Internet Tablet anymore and it's just a smartphone but when you use it, you really feel like you're using a device that is more than a smartphone.