If you want to use your 48 number/SIM abroad then you'll need to keep buying monthly membership plans in order to be able to use EU/EEA/UK roaming services.
If you don't need to use it for for 9 months then you can not bother buying a monthly membership plan and when you're back after 9 months contact 48 support to get your account/number active again.
But note that you'll lose any cash credit on your account if you don't buy a plan for 8+ months.
See here:
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 decide to not buy a plan for a few months while abroad then make sure to disable membership plan auto-renewal.
If you need to contact 48 support about this then see the links in my signature below.
