The X1 is an arc-slider phone with the Windows Mobile 6.1 Operating System. It is Sony Ericsson's first mobile phone to feature Windows Mobile. Device also has Java virtual machine (JBed) and supports JavaME that is claimed to have richer set of features than typically available.

The phone features a three-inch touchscreen overlaying a QWERTY keypad which emerges when the user slides the touchscreen face upward, much as in the HTC TyTN II, although the X1's touchscreen slides out in an arc. Its touchscreen is a 65,536-color TFT WVGA display. It has a 3.2 megapixel digital camera which records video at thirty frames per second in VGA (640x480) quality.

There is also a secondary front facing camera for videoconferencing that is of QCIF format. Connectivity options for the phone include: mini-USB; wireless LAN 802.11b/g; Bluetooth 2.1 with A2DP, FTP, and HID; EDGE; and quad-band GSM, UMTS, HSDPA, HSUPA, and HSCSD. The X1 has 512MB of internal memory (400MB free), which is expandable to 32 gigabytes using High Capacity microSD cards, although currently only cards up to 16 gigabytes have been released by SanDisk. The phone also features A-GPS for navigation.