You will be billed overage charges on a per-use basis, at the effective rate for the country visited.
Note: The amount billed for data overage and for usage of the Daily Traveller Pass is automatically limited to $100 per billing cycle.
Upon reaching this limit, data usage will be suspended until your next billing cycle. However, you can remove this limit at any time in your Customer Centre or the User Centre + app, in the Roaming Usage Limits section.