volutionary path but still did not need to jump all the way to full-scale cdma2000 "3G" speeds. But then such solutions were already becoming available, and they did not require 3G. Instead, a number of less-costly technologies rolled out. These offered improved data performance, compared with plain old 2G, but without new frequencies or completely new base stations. They were nicknamed "2.5 G", the halfway step to 3G. And network operators worldwide jumped on them. In North America, for instance, some of the original cellular operators had developed a service called cellular digital packet data (CDPD) that even worked in conjunction with first-generation analog networks. CDPD carried data, in the form of IP packets, on vacant channels in the 800-MHz cellular band. Its 19.2- Kbps burst speed was not spectacular, but it was sufficient for many appli- cations such as e-mail and text message delivery. Although it was far from uni- versally deployed, CDPD was installed in most major American cities. CDPD was not even 2.5 G technology, but it pioneered the cellular data market. The GSM world has its own migration path. Beginning in 2000 or so, GSM networks have begun to roll out general packet radio service (GPRS). This adapts GSM's digital transmission scheme to allow peak data rates in the 50-100 Kbps range, using connectionless packets and thus "full-time" connec- tivity versus the circuit-switched model of telephone calls. Its key technical fea- ture is the ability to access all eight time slots in a GSM TDM channel, thus theoretically allowing it eight times the burst rate of a regular call. GPRS is fol- lowed by EDGE (Enhanced Data Rates for GSM Evolution, although "GSM" was originally "Global"), which triples the data rate of GPRS by using a more advanced modulation scheme. Another approach, HSCSD, for high-speed circuit-switched data, simply takes up to four GSM telephone call time slots and aggregates them into a single data channel of up to 57.6 Kbps, provided the bandwidth is available. This lacks the full-