The tri-band GSM (900/1800/1900 MHz) Mio 8390, which is based on Microsoft's Windows Mobile for 2003 operating system. The Mio 8390 is the sequel to the Mio 8380, the company's first smartphone.

Like with the earlier Mio and some other current Microsoft-based smartphones, such as those from Motorola and Samsung, the clamshell 8390 features two displays, an external one at the back of the top half of the clasmshell for Caller ID, battery life, time and signal indication and a 2.2-inch screen on the inside of the clamshell. The internal display features a 176 x 220 resolution, standard for Microsoft smartphones, that is capable of supporting an impressive 262,144 colors. Most high-end handheld and smartphone screens only support color depths as high as 65,536 colors.

The smartphone runs on an Intel Dalhart (PXA262) 200MHz processor, and has 16MB of memory, 32 MB ROM, and a Secure Digital slot for memory expansion, as well as a VGA (640x480 pixel) camera that is good for 15s clips of video and unlimited playback, as well as pictures with 8x digital zoom. The camera also features a four-shot burst mode as well as a mode for night time use to improve picture taking under bad lighting. In terms of power, the 8390's Li-Po 1050 mAh battery delivers 100 hours standby and up to 3 hours talk time.

Users can also listen to MP3 and Windows Media audio files on the 8390. The device also supports 40-tone polyphonic ringtones and MP3 ringtones. A nice feature called flight mode turns off all the communication aspects of the smartphone so users can use the device on a plane.

The earlier Mio was based on an older Microsoft operating system and a lower-resolution digital camera. Unfortunately, the new one doesn't include Bluetooth like the previous edition, so users will still be unable to use Bluetooth-enabled wireless headphones. The 8390 measures 99 x 51 x 24 mm, not much less than the 8380. It weighs 125 grams.