I seem to remember Optus are a funny about BIS+BES stuff. But a quick test
visit the Optus BIS portal
https://bis.ap.blackberry.com/html?brand=optus sign him up & test an email address. in thoery it should work as it's RIM who pop's the email & send it to the device.
Richarddg, yeah iot works a treat. I also got them to add the BIS codes to my sim, so I get the BIS browser option, handy in case the proxy server goes down ;-)