Let me give you all an analogy. A 2G unlimited data card is like a hard-seat train ticket. Even if the train speeds up, you can still use it, but the service you enjoy remains that of the hard seat.
In fact, there's no need for further debate. A 2G card, especially a data card, definitely cannot use the 3G service access point. However, you can still register and use the 3G network (around October) without any issues! But if you switch to a 3G access point, one outcome is that you won't be able to connect, and another outcome is that you will be charged based on data usage (unless you have added your own package). So everyone, there's no need to get worked up!