domains .com vs .com.au
Basically .com.au identifies Australian based business domains whereas, .com could be used globally. Technically speaking, websites depend on two things; one is domain name registration and other one is web hosting. Even though .com.au is registered in Australia it could be hosted in the US since comparatively US hosting companies are very cheap. An average web hosting price varies from 1 dollar per month to 6 dollar per month with unlimited bandwidth usage. Australian domain names will cost around 12 dollar per year and registration requires Australian Business Registration or similar regulations. Hosting decision depends on users’ geographical position as well.
Probably the most important effect a .com.au domain has is that some search engines filter their results according to where the searcher lives. Example, Google indentifies your position and display the results accordingly. If you search from Australia for mobile unlimited plans it would bring Australian based providers on the top search results. In this context .com.au domains have chances to come to the top in the search results.
Over time you will find that depending on your product, .com.au domains may rank higher in Australia than international domain names. This is important if your market is solely in Australia.
What if your market is global? Then a .com may be more appropriate for you. For example, our domain name is a .com domain, because we can and do provide our services worldwide, even though we are an Australian business based in Australia. We want our concern to be recognized as a global internet business and so we chose the .com domain.
Having said that, there is no reason why you can’t have both. It is certainly possible to purchase both the .com and the .com.au versions of your domain name and have them both point to the same website. This could be either domain parking or domain addon.