How to listen voicemail whilst roaming in abroad?

Hello. Whilst I travelled to Japan I received a message to call 121 to listen a voicemail. I called 121 and then received a call back from 121, however it ask me to press 1 to listen voicemail. I pressed 1 by keypad, however It was a call back therefore pressing 1 was not processed as a command... How to listen the voicemail whilst I travel outside the UK, EU and USA? When I was in the UK, calling to 121 worked to listen since it was connected directly though. Regards.