I have travelled on some backpackers buses but haven't had any first hand experience with Oz Experience. With other buses I never felt compelled to go out partying but it was nice to know that there were plenty of drinking partners when I wanted a night on the town.
All the main mobile operators have very good coverage along the east coast and in the major cities, although Telstra has the best coverage in the more remote areas. Based on your itinerary I would go for the mobile company with the cheapest pre-paid plans.
Vodafone and
Virgin Mobile have the best value pre-paid deals and most backpackers use Vodafone.