For Telstra customers that simply must have access to their mobile number whilst overseas, Telstra's International Roaming charges are as follows:
Prepaid users: Telstra International Roaming Plus Pack
|30 Day Expiry|
Postpaid users: Telstra International Day Pass
You receive unlimited inbound/outbound calls & SMS each day & 500MB of data. The drawback with Telstra's International Day Pass is that it expires each day.
A typical user may do perfectly well with 500MB on most days, but it is highly unlikely they will not exceed this quota at least on a few days of their trip.
Once you exceed the limit you will trigger another $10 payment for 1GB of data that is valid for 31 Days.
In practice it works out $10 day + $10 per GB ($5 a day for NZ).