The Samsung Z400 looks and feels similar to the Samsung D600 but there are some significant differences. You'll immediately notice that the Z400 is a compact and light 3G phone. It's also actually of the few slider phones that supports 3G (others include Nokia's N80 and 6280, and the forthcoming Sony Ericsson W850i).
The Z400 measures 49 by 97 by 19mm and weighs 107g. On the top-left side of the front section of the phone there's a small 0.3-megapixel (VGA) camera, which allows for video calls via a 3G connection. The rest of the front section looks similar to the front of the D600, with a 240x320-pixel screen displaying 262,000 colours, a navigation key with a silver OK button in the middle, two soft keys either side of that, and send call, cancel and end call keys underneath.
Unlike some Samsung phones the OK key in the middle of the navigation button accesses the menu and not the Web browser, which means you're less likely to browse the Web when you actually want to see the menu. Another change is a small plastic ridge above the navigation button that lets you push the slider up without needing to touch the screen or push any buttons by mistake.
On the left side of the phone there's a dedicated volume button and further down an expandable microSD slot that is easy to access and protected by a cover. On the right side there's a charging port that doubles as a headset port, which is protected by a sliding cover. Further up on this side is a dedicated shortcut key that gives you access to calls, messages and Internet browsing.
Once you slide the Z400 open you see the alphanumeric keypad. We found the keys pretty awkward to use because they feel small under the thumb and are curved, making it harder to press the right one. On the back of the open slide there's a 2-megapixel camera with a relatively large portrait mirror.
We like the fact that the camera is protected behind the slide as this avoids scratching it but we're disappointed that there's no flash or LED photo light. As for the slide mechanism itself, it's similar to the spring-mounted slide mechanism on the D600, but the phone feels more clunky when you slide it open and shut.
The Samsung Z400 is a 3G phone that lets you make video calls and access data over the air at near-broadband speeds. If you're in an area that only has 2G networks, it supports both GPRS and EDGE (see the Mobile Phones Buying Guide for more on network standards). Video calling and Web browsing worked well on the phone and the video call interface is straightforward to use. Simply dial a number, go to Options and select Video call.
There is a 2-megapixel camera on the back for taking pictures or video of something other than your face. You can access the camera interface using the dedicated camera button on the top right-hand side. This button won't let you shoot pictures, though. If you want to take a picture you have to use the OK button in the middle of the navigation key.
The camera interface gives you the option to shoot several photos in quick succession or shoot in a mosaic style. You can also select from several effects, including turning the image black and white or inverting the colours.
You can store large amounts of photos, as well as MP3s, on the microSD slot. MP3s can be played on the built-in MP3 player. You can adjust the play mode and volume on this, but it is basic compared to those found on the Sony Ericsson Walkman range of music phones.
A small but interesting feature is the Connection Vibration mode, which vibrates the phone when you connect or disconnect from a call. This comes in handy when you're waiting for a call to connect but don't want to hold the handset to your ear, or when you're in a noisy environment and can't hear whether you've connected.
As with the D600 you can connect the Z400 to a TV and view your photos on the big screen. You can also put the phone in offline mode so that you can use it without connecting to a network. This is useful if you want to listen to the MP3 player without wasting battery or use the phone in an area that doesn't allow mobile phones.
Other features include MMS and SMS messaging, a document viewer, an email client, a Web browser, Bluetooth, a voice recorder, Java games, a calendar, an alarm, a task list, memo, a world clock, a calculator and a converter.
Audio on calls was clear and we could hear people without needing to raise our voice or press the ear speaker hard against our ear. Video calls were as clear as can be expected over a 3G connection and the images were recognisable. Video calling in general still doesn't give crystal-clear images, though.
The 2.0-megapixel camera took clear photos when we held it very still but images were blurred if we weren't holding it steady. There's no flash, so taking photos at night was impossible without an external light source.
Battery life is quoted at around 3 hours 40 minutes talk time and up to 320 hours standby time.
Edited by Mary Lojkine
Additional editing by Kate Macefield