If you want to use roaming services over there then you need to have an active membership plan.
Note that only sending/receiving texts work in Australia and you need cash credit to pay for them (along with an active membership plan).
You won't be able to make or receive calls or use mobile data.
See here for details.
If you want to use mobile data and your phone supports an eSIM then this might be an option:
As long as you buy a monthly membership plan every 6 months your account will not become deactivated.
Topping up your cash credit balance won't help in this regard - you need to buy a membership plan.
See here for details:
7.2 In addition to the circumstances set out in Section 7.1 above, we may suspend
(i.e. bar), restrict or end the provision of the 48 Services (in total or in part) if you
choose not to purchase top up credit or make a chargeable use in respect of your
Account for a period of 6 months.
7.3 Where the 48 Services are suspended because you have chosen not to purchase
top up credit or make a chargeable use in respect of your Account for a period of 6
months, we will remove any credit on your Account after a further 2 months and credit
will not be recoverable. Your service will then remain suspended for a further 5 months
and can be reconnected at any time during this period. When the suspension period
ends your service will be disconnected, this agreement will end and your number will be
immediately lost.
If you need to contact 48 support about this then see the links in my signature below.
