Four new models planned BOSTON – Hewlett-Packard Co. (HP) plans to update its line of iPaq PDAs (personal digital assistants) on Monday with four new models, according to a member of HP’s public relations staff.The new models will help HP continue to gain ground on PalmOne Inc. in the PDA market. HP’s market share in this category has grown over the past several quarters as it has introduced new devices across a variety of categories, from low-end devices costing about $300 to powerful systems that offer Wi-Fi capability and Bluetooth personal area networking technology.The overall PDA market has been declining for several years as consumers have lost interest in stand-alone PDAs that can only handle basic personal information management (PIM) functions. Most mobile phones can handle basic PIM functions such as contact lists and calendar appointments, and most users don’t want to carry two devices. Analysts have advised PDA vendors to focus on the high end of the market with multimedia devices or converged devices that offer some type of communications technology. PalmOne’s Treo 600 smart phone and Research in Motion Ltd.’s BlackBerry wireless e-mail devices have been the most popular sellers over the last six months, according to market research from IDC and Gartner Inc.Specific details about the new devices were unavailable. HP plans to host an event in London on Monday to discuss its mobile strategy and provide details about the new products.The company also plans to introduce three new Compaq Business notebooks on Monday for the small and medium-size business market. Technology IndustrySmall and Medium Business