Message bank on Iridium phone.

Need some advice please from the gurus.
I have an Iridium 9505A sat phone which used to be on a contract. The contract has expired and now I just use my Telstra Next G sim card with international roaming enabled and everything works fine except for text message bank. Our usual practice is not to have the phone on during the day (that's why we go bush in the first place!!!) but let people know we put it on for an hour or so in the evenings to check for messages. If there is something urgent we will call back.
On a recent trip we got no messages on the sat phone but when I put the sim card back in my normal mobile at the end of the trip there were 2 text messages waiting that had been posted some days ago.
Do I need to set up something on the Iridium to have message bank. I had assumed it would be on the sim card and work like my normal mobile.

Thanks in advance for any advice.
Cheers
Dave