Many recent wireless projects rely on an increasingly popular technology known as 802.11b, or Wi-Fi (short for wireless fidelity), an inexpensive and popular networking standard that uses an unlicensed portion of the radio spectrum. It’s cheap, fast and spreading like a virus, especially in high-tech centers like New York, Seattle and Silicon Valley in particular, where the abundance of early adopters and evangelists has produced the greatest concentration of “hot spots.”