Coverage and performance
Mobile broadband coverage has steadily increased over the years as telcos build more towers and upgrade infrastructure to increase reliability. 3G reception coverage is also increasing, though for many telcos GSM coverage is still prevalent outside of metropolitan city areas.
The coverage and performance you experience is largely dependent on your carrier. Essentially, you pay for what you get: Telstra is widely known as providing the best mobile broadband coverage and performance, but it charges premium access fees. Conversely, 3 Mobile provides good value plans and pricing, but often lacks the coverage, reliability and performance of other major telcos, even within inner-city area.
The most important thing to look at when choosing a wireless broadband provider is whether it has coverage in all the areas you might want to use your connection. If you're in a marginal reception area, such as the outlying areas of major cities, you may find the connection drops out occasionally, as weather patterns and other interference wreak havoc with your connection. You don't want to be caught with an Internet connection that only works half the time.
Pricing and quota
Mobile broadband pricing has dropped dramatically in recent years. Speed, coverage and equipment costs should all be taken into account when tossing up between wireless broadband and fixed-line services, but if you want mobile Internet, the prices are certainly attractive. All the main telcos offer prepaid wireless broadband, which offers extra flexibility. Some also provide discounts if you bundle multiple services like mobile broadband, a mobile phone as well as any home phone or fixed-line Internet services in the one account.
Download quotas aren't as important for wireless broadband plans as they are with fixed-line services. Though you might need 30 or 40GB at home to download movies from iTunes, you are unlikely to do the same while you are out, so 5 or 6GB might be all that you need to watch trailers, download the occasional song and ensure you get all your e-mail. For most people, however, even 500MB to 1GB of data is enough for light Web browsing and e-mail. You should consider how much you're likely to download and choose a plan accordingly.
Like fixed broadband services, many mobile broadband services either charge supplementary costs or shape download speeds if you exceed your quota. Excess costs are often exorbitant, so choosing a plan which shapes your speed is the ideal way to avoid a nasty shock when your bill arrives.