Once you've purchased a $9.95 starter kit, you can top up on the MAX plan with $10 or more of credit. Until that credit expires, you get 5MB of data a day, with excess usage charged at 2 cents per megabyte. (Note that gotalk rounds charges to the nearest 5 cents.) The big caveat here is that gotalk uses Vodafone, which doesn't enjoy a great network reputation right now.
The other selling point for the MAX plan is cheap international calls, with some calls attracting only a 15 cent flag fall. We looked at a similar '0 cents per minute' deal for international calls from Lebara back in March. Gotalk's offer covers rather more countries (67 by its own count), though those rates only apply to off-peak calls (between 11pm and 11am). Outside that period, the flagfall is 30 cents and the rates vary heavily by country.