Have a look at www.optus.com.au/blackberry
. The cap includes up to 50MB of email usage. * Optus Zoo/ WAP GPRS browsing and downloading charges excluded. Special Optus Zoo /WAP offer valid to 30/09/05. See terms and conditions for details. WAP/GPRS $9.90 cap offer does not apply.
With Telstra its a little different. Their monthly fee includes unlimited BlackBerry specific traffic. ie email. Anything that is not specific to BB, ie WAP, SMS, Voice calls are charged extra. If you are running BES, all MDS traffic is included which is a great deal with Telstra. Plus its only $49.95 per month plus voice.