@SimonBur_580006 If you do not use your Smarty account for 180 days, it will close and the sim will deactivate and your number will be lost. You will therefore need to buy a Smarty plan at least once every six months (but you won’t be able to use it over there). If you put some credit on the account you could send a text maybe just to show that sim has been used (belt and braces approach)
