You've typed a sentence into the subject line of your post but it's been cut short and you've not put any details into the actual body of your message.
Are you asking about billing add-ons for roaming? The roaming facility is free of charge and is what enables your phone to connect to foreign networks, and thus avoids you not having coverage abroad.
What billing add-on are you (presumably) querying? If you had a daily or weekly pass in Australia, that will naturally expire and you can purchase a new one in Dubai when you arrive.
