HDML (handheld device markup language) It uses hypertext transfer protocol (HTTP, the underlying protocol for the Web) to allow for the display of text versions of webpages on wireless devices. Unlike wireless markup language (see WML), HDML is not based on XML. HDML also does not allow developers to use scripts, while WML employs its own version of JavaScript. Phone.com, now part of Openwave Systems, developed HDML and offers it free of charge. Website developers using HDML must recode their webpages in this language to tailor them for the smaller screens of handhelds.

I-Mode A wildly popular service in Japan for transferring packet-based data to handheld devices. I-Mode is based on a compact version of HTML and does not use WAP (see WAP), setting it apart from other widely used transmission methods. I-Mode's creator, NTT DoCoMo of Tokyo, agreed in November 2000 to pay $9.8 billion to buy 16 percent of AT&T Wireless. Since then, AT&T Wireless has talked about bringing I-Mode to the United States by the end of 2001--a daunting prospect that requires the rebuilding of U.S. wireless networks, analysts say. DoCoMo is developing a version of I-Mode that supports the WAP standard.

Integrated Digital Enhanced Network (iDEN) A technology that allows users to access phone calls, two-way radio transmissions, paging and data transmissions from one wireless device. Developed by Motorola, iDEN is based on TDMA. Services based on the technology are available in North America (offered by Nextel), South America and parts of Asia (see TDMA).

Kbps (kilobits per second) A measurement of bandwidth in the United States.

Packet A chunk of data that is sent over a network, whether it's the Internet or wireless network. Packet data is the basis for packet-switched networks, which are under development in the United States as a faster, more reliable method of transferring wireless data than a circuit-switched network. Packet-switched networks eliminate the need to dial in to send or receive information because they are "always on," transferring data without the need to dial. The packets that hold data depend on the size of the data involved; "chunks" are broken down into an efficient size for routing. Each of these packets has a separate number and carries the Internet address for which it is destined.

Packet-switched network Networks that transfer packets of data (see Packet).

PCS (personal communications services) An alternative to cellular, PCS works like cellular technology because it sends calls from transmitter to transmitter as a caller moves. But PCS uses its own network, not a cellular network, and offers fewer "blind spots"--areas in which access to calls is not available--than cellular. PCS transmitters are generally closer together than their cellular counterparts.