the you spend some time defining what a typical 2G and 3G connection looks like to your end users, and then you replicate that with existing tools. There are very, very many open source solutions to adding latency, jitter, throttling bandwidth, and replicating packet loss. in fact, I'd argue that coming up with a few solid definitions of what a 2G and 3G connection look like is far more accurate than running tests over one dongle "IRL"