Whats the difference between 1G, 2G, 3G wireless networking systems?

First, about cellular generations. First 1G service was based on a TDM voice infrastructure -- built around class x switches and 64 kbps slots. It had data, but circuit switched over a 64Kpbs voice bearer.

Second, 2G service had the same switched TDM backbone, but added a true Data Bearer and a digital voice bearer. Data rates were still limited to the max 64kbps of a single time slot.

2.5G added a packet bearer to the mix, still limited to 64kbps slots.

Third generation (3G) changed the backbone slightly to allow a full T1 or E1 or J1 to be consumed by a data sub-scriber, but is still based on an ISDN style backbone. Sure you have packet switched data, but its carried over a traditional TDM backbone. There still a circuit voice backbone and while the data rates are high enough for VoIP, the latency of the data service is to great to base all of the "bearer services" on it, so you still have circuit voice, circuit data and packet data bearers.

Finally, 4G systems will utilize a packet infrastructure rather than a traditional telephone architecture. Services will be horizontally layered on top of a proper low latency, QoS enabled packet switch (read IP) infrastructure. Gone will be the circuit voice and circuit data bearers.

So "G" has more to do with the infra-structure and less to do with the data rates. The data rates over the air are driven by the organization of the infrastructure and other than that have little to do with what generation they are.

In that sense, this NexTel trial is a 4G trial.
K A Solaman