This might appear to be a simple question... but can't seem to find any definite answers on this...
From what I can gather, the 4G LTE newtorks operate on different frequencies in some countries (i.e. USA vs Australia). So, I assume that if I took my skyrocket to Australia it won't work on the 4G lte network there... but what network would it work on - 4G or 3G or will it be just 2G? Not entirely sure whether "quad band" phones cover the the frequency differences between 4G, 3G and 2G.
Will there be any 4G LTE phones that will work on all LTE frequencies any time soon?
I don't believe Australia has LTE yet. EVen within US, AT&T and Verizon LTE phones can't roam to each other's network. Both are using some bands of 700MHz. European market should be 800MHz and some other bands. LTE is at its infancy. Roaming is not possible at this time. The phones you can purchase from US carriers only support AT&T bands of LTE,
However, for Skyrocket, you should still be able to use HSPA+ in Australia if the local carrier uses 850Mhz band (some Australia carriers do use 850Mhz). In Europe and Asia, it is pretty much 2G GSM only (that's the only radio that supports quad band).