Questions about Telstra Next G & VOIP while on the road

I have been reading most of the threads about Telstra's Next G Network as well as anything on VOIP. If this topic has been covered either in full or in part I beg your indulgence.
I have a new caravan on order and expect to hit the road for another trip from Wollongong NSW across to South West WA later in the year.
I am researching the best, most convenient and most cost effective way of setting up comms for data and voice.
At home, I have a fixed Telstra line, Internode ISP and an Engin VOIP voice box. This gives me 10 cent untimed national calls to fixed phones, reasonable rates to mobiles and very attractive international rates (son in London)
I am thinking of swapping from Internode to a Telstra Next G plan and using the "Toaster" wireless modem for Internet access and Engin's Softphone for VOIP. Engin will swap me from the voice box to Softphone and back again whenever I request it.
To make or receive calls, my PC and modem will need to be on and connected to the internet.
All calls TO my VOIP number are treated as calls to my Wollongong address no matter where I happen to be.
Is anybody using a Telstra Next G plan with VOIP and if so, what sort of voice quality do you get in remote areas. I am led to believe voice quality is very dependent on the quality of the broadband connection.
Should I talk to my caravan manufacturer about pre-wiring an external antenna for the Telstra "Toaster" modem or are the standard "rabbit ears" sufficient?
PS I will have a Next G mobile and even have an old sat phone which could be resurrected for emergencies (at a cost).
Note I also posted this on Caravaners Forum

Regards,

Rosscoe