Dynamic DNS on Telstra NEXTG Network
If you're trying to set up dynamic dns and you're on the Telstra nextg mobile broadband network you'll probably find that it doesn't work first go.
This is because Telstra allocates nextg customers a NAT'd IP address that is not externally accessible. As such, even if you've got your dynamic DNS client updating correctly it'll be updating with a Telstra public IP address that is not directly associated with your network.
Fortunately you can call Telstra and ask them to apply a code on their system such that your mobile broadband device get's allocated a publically accessible dynamic IP address.
The code that you need applied to your account is: GPTEXB3
Be sure to have your SIM card ready as they'll ask for for the 10 digit code ending with N that is printed on the SIM.
Afterwards, you'll need to alter the APN settings on your broadband device from Telstra.Internet to Telstra.Extranet.
Apparently bigpond customers are allocated a publically accessible dynamic IP address by default, so if you're on bigpond mobile broadband, you shouldn't have to do any of the above.