3 hours ago
an hour ago - last edited an hour ago
You can't.
There's no special cheap plan for this purpose.
If you want to keep using your number then you need to keep buying your normal monthly membership plan.
If you don't buy a plan for 6 months then your account will become suspended.
If you don't buy one for 13 months then your account will get deleted.
The terms and conditions explain this.
What country are you in because in some countries roaming services require an active membership plan and cash credit to pay for certain services and in some countries some or all roaming services are not available at all.
If you need to contact 48 support about this then see the links in my signature below.