T-Mobile's GPRS data service is priced well below the others we tested-and for good reason: We experienced low transfer rates and high latency on T-Mobile's network.

We tested T-Mobiles GPRS network using a Sony Ericsson GC79 PC Card, which T-Mobile sells for $200. The GC79 combines a GPRS radio with an 802.11b radio, which is a handy and slot-saving paradigm for machines that lack built-in Wi-Fi.

Click here to read the full review of T-Mobile.