A specialized version of HTML designed to enable wireless pagers, cell phones and other handheld devices to obtain information from Web pages. HDML was developed by Phone.com (formerly Unwired Planet) before the WAP specification was standardized. It is a subset of WAP with some features, not included in WAP. AT&T Wireless launched the first HDML-based service in 1996.
The Handheld Device Markup Language (HDML) is a markup language intended for display on handheld computers, information appliances, smartphones, etc.. It is similar to HTML, but for wireless and handheld devices with small displays, like PDA, mobile phones and so on. It was originally developed in about 1996 by the company that became Openwave.