Wireless data services like General Packet Radio Services (GPRS) and Code Division Multiple Access (CDMA2000/1X) are widely available today. If you're based in the US, check out AT&T, Cingular, or T-Mobile for GRPS, and Sprint or Verizon for CDMA2000. Newer "third generation" higher-speed data services like GPRS EDGE and CDMA2000 1xEV-DV are now being rolled out to more limited serving areas, starting with selected major cities. Check provider websites for coverage maps to see which WWAN services are available where you live, work, and travel.
WWAN services are typically delivered to "smart phones" and PDAs sold by cellular service providers and their retail partners. But you can also purchase WWAN PC cards to add to your laptop. Unlike Wi-Fi cards that can be used in just about any hotspot, WWAN devices must be provisioned specifically for access to your service provider's network. Your service provider will take care of billing for roaming access to other provider networks. So start by finding a service provider with the coverage you need, then choose a compatible WWAN device and service package.