Windows Mobile is an operating system specifically designed for handheld devices. It's a mini version of Windows that uses the familiar Microsoft interface.
There are two types of devices that Windows Mobile is used on. The first is a connected device that combines a handheld computer with a mobile phone, enabling you to make calls and download data over mobile networks. The second is a standalone device that doesn't have mobile phone functionality.
Aside from connectivity and keypad differences, the two types are similar in terms of features. The Windows Mobile interface lets you transfer Microsoft Outlook contacts, calendar, emails, tasks, Internet Explorer favourites and media fairly easily. It also lets you install third-party programs like Skype, so that you can make Internet calls over a Wi-Fi connection, assuming the device has a built-in or external WLAN adaptor and a fast enough CPU.
Connected handhelds are useful because they give you access to phone calls, MMS messaging and SMS messaging on the move. The other advantage of a Windows Mobile device with network connectivity is that you can get emails sent straight to it via the direct push system. This forwards messages from your email server to your handheld device so you're never out of touch.
Standalone devices are primarily used as organisers that hold contact information and let you schedule appointments or take notes. As with the connected handhelds, these devices can feature Bluetooth, infrared and Wi-Fi connectivity so you're not completely cut off from the outside world. You can also synchronise any Windows Mobile device with your PC, so you can still transfer your emails to the device -- you just can't do it on the move.
Two factors that greatly affect the user experience are the shape and feel of the device, particularly the size and shape of the keypad. You need to check whether you feel comfortable holding and using it before you buy it. Keep in mind that handheld devices are renowned for being chunky and many of them won't fit in your pocket.
Irrespective of which type of device you go for, the most important features to check are the CPU speed and internal memory. As with PCs, the type of CPU is also important, and overall you should treat a handheld like a PC -- the better and faster the CPU, the better and faster the handheld. In terms of internal memory, we find that around 50MB is satisfactory for running basic applications. Many handhelds also have a slot for a memory card, which is useful if you want to store music or videos. For more advice on choosing a handheld, see our Handhelds Buying Guide.