The DX900's main claim to fame is that it's the first Windows Mobile handset to support dual SIM cards. Why would you want a dual SIM phone? If you have to ask the question then a dual SIM handset is probably not for you. For others, though, support for dual SIMs is handy because instead of carrying around separate mobiles for work and personal usage, you can get the same job done with a single handset. They're also useful if you travel a lot and want one SIM for calls within your home country and another local SIM for use abroad in order to avoid racking up horrendous roaming charges.
Despite the world's first claim, the DX900 has actually been available before in a slightly different guise. This is because it's basically a re-branded version of a handset that was previous released by E-Ten under the Glofiish brand. Acer snapped up E-ten last year and has now re-released the phone as its first own branded handset. However, shortly it's due to be joined by new models including the F900 and M900.
Looks-wise the DX900 isn't exactly what you'd call handsome. It's rather large and chunky and at 143g is quite weighty too. You'll definitely notice it when it's tucked away in your pocket. However, it does feel very well built and its sturdiness gives you confidence that it'll stand up to a few knocks and scrapes.
The slightly rubberised feel to the rear of the case also makes it quite tactile to hold and means it's not likely to easily slip from your grasp. Unlike manufacturers like HTC who use the miniUSB port to double up as the headset jack, Acer has instead kept the two separate. This means you can still take calls or listen to music when the handset is being charged or synced with your computer. However, the hands-free connector is a small 2.5mm socket rather than a normal headphone jack so you won't be able to use your own headphones with it unless you invest in an adaptor.
Of course, the key difference between this handset and its rivals is that it allows you to have two SIMs installed and active at the same time. That said, although there are two slots, they're certainly not equals. Only the first slot supports 3G/HSDPA, as seconds one is limited to 2.5G data speeds, which seems like a rather puzzling limitation to us. Once the SIMs are installed you do get two indicators on the home screen to show you the relative signal strengths of the two mobile networks.
Acer also includes an application that lets you control how the SIMs are used. This lets you easily switch between the two mobile networks, but also allows you to turn off one completely - handy if you want to switch the work SIM card off on the weekends or during holidays without having to actually physically remove it from the phone.