Cellular networking offers the following downstream speeds (for activities such as receiving email, downloading files via FTP, and surfing the Web):
Upstream speeds (for activities such as sending email, using FTP to upload files, and uploading documents to web sites) are generally less than the download speeds, anywhere from 9.6 Kbps to about one-half the downstream speed.
One of the fundamental limits on cellular networking is the price of data. Typical packages offer a bucket of data with coverage charged per kilobyte over the limit. Table 8-1 shows some examples based on current U.S. pricing.
A busy user can blow through 20 megabytes in a couple hours of web surfing and email. So heavy users should opt for an unlimited pricing plan, or carefully plan out their usage to take advantage of (free, if possible) Wi-Fi hotspots and use the cellular service only when absolutely necessary (such as sending out an urgent email while sitting on a runway).
Even with a data allotment that you're comfortable with, service can be spotty, though coverage is most comprehensive in densely populated areas (especially Europe and Asia). However, in a densely populated area such as New York City, buildings can interfere with the signals, and many simultaneous users can limit the performance of the network in a given area.
As tempting as it is to chalk up performance problems to early adoption doldrums, the old maxim still stands: let the buyer beware. If you knowingly purchase poor service in the hopes that it will improve over time, keep in mind that there is no guarantee that it will. When in doubt, seek the opinions of others; the Usenet hierarchy alt.cellular.* has many newsgroups devoted to specific carriers where you can read about peoples' experiences (you can read and post to these newsgroups through Google Groups at http://groups.google.com). Be sure to get service from a provider who offers a complete refund, no questions asked, within a reasonable trial time (some providers offer 15 days, which is too little, so try pressuring the sales person for a 30-day trial).