3.5G (or any cellular data connections) weren't built for low latency. 200-400ms sounds like a fair expectation for 3 or 3.5G. 4G and LTE or whatever they call it these days *may* have lower latency.

Speed does not always correlate with latency. You can have a 10mbps connection with high latency, or a 56k connection with low latency (like 20ms pings on average)