Hugh Pickens writes "The NY Times reports that more than 40 percent of all smartphone owners and 80 percent of iPhone users use their mobile devices to get turn-by-turn directions driving down sales of traditional standalone GPS units from companies like TomTom, Garmin and Magellan. During the first quarter, TomTom said it shipped 29 percent fewer GPS units compared with the period in 2008 while Garmin's unit sales fell 13 percent from the previous year. While smartphones are susceptible to interruptions from incoming phone calls and using the mapping features for a long time can chew through battery power, the list of the smartphone's shortcomings is dwindling as some of the latest navigation applications offer voice navigation and take advantage of the phone's always-connected state to offer real-time traffic updates, directions to contacts in the phone's address book and more. 'I've not stopped using a GPS because I never bought one in the first place — they are expensive and inconvenient,' says Steve Weller. 'Now with the iPhone, I will actually use GPS — and the 10 other functions it replaces.' The traditional GPS device companies are trying to adapt, seeking to expand their reach into the smartphone market. TomTom recently announced that it would introduce a portable navigation application for the iPhone that would feature turn-by-turn directions and audio prompts. 'The simplicity of having one device and not needing to pull the Garmin out of my glove compartment is enough,' says Andrew DiMarcangelo. 'I want to get into my car and do as few things as possible.'"