At a new manufacturing plant outside San Diego, round-the-clock shifts fill pallets with wireless phones ready to ship to Sprint and other providers. The products in question are thin circuit boards destined for the next generation of handheld devices to access the Internet. Each circuit board inside this Denso International plant reveals why handhelds have become wildly popular: They blend humans and machines perhaps better than any prior invention. Analog chips, which render emotionally toned voice, share the board with digital signal-processing chips that are brilliant at manipulating data. Natural human communication and data-it's a compact and capable combination that is ready to fuel the next stage of network development: the mobile Internet.

The circuit boards rolling off the Denso line are harbingers of an explosion that may dwarf the growth of PCs. America Online took more than 10 years to reach 20 million subscribers. NTT DoCoMo, the Japanese company with the country's largest Internet portal, expects to reach that rarefied stratum in less than two years for subscribers of its mobile data service. Within several years a billion people-1 in 6 on the planet-are likely to access the Internet through portable wireless devices, according to analyst and company estimates. "They used to say every home will have a PC," says Dave Oros, CEO of wireless startup Aether Systems. "I believe every pocket will have a handheld."