I access the internet via an O2 mobile 4g dongle. Occasionally, like now, the coloured light changes to show that it is operating on 3g. I notice no discernable difference in speed or performance, so what's this 4g all about?
It'll probably use 4G when it needs to, and switches back to 3G when it doesn't. It's all about faster communication of data over the mobile phone airways.