This article is about the iPAQ PDA; for the iPAQ Desktop Personal Computer, see iPAQ (desktop computer). For the NASA center, see Infrared Processing and Analysis Center. iPAQ presently refers to a Pocket PC and personal digital assistant first unveiled by Compaq in April 2000; the name was borrowed from Compaq's earlier iPAQ Desktop Personal Computers. Since Hewlett-Packard's acquisition of Compaq, the product has been marketed by HP. The devices use a Windows Mobile interface. In addition to this, there are several Linux distributions that will also operate on some of these devices. Earlier, units were modular. "Sleeve" accessories, technically called jackets, which slide around the unit and add functionality such as a card reader, wireless networking, GPS, and even extra batteries were used. Latest versions of iPAQs have most of these features integrated into the base device itself. Hewlett-Packard introduced the first smartphone iPAQ Pocket PC that looks like a regular cell phone and has VoIP capability. The series is the HP iPAQ 500 Series Voice Messenger. HP's line-up of iPAQ devices includes PDA-devices, smartphones and GPS-navigators. A substantial number of current and past devices are outsourced from Taiwanese HTC corporation.