Public Green Phone on the Shinkansen

I travelled on the Nozomi Shinkansen from Tokyo to Hiroshima in July and noticed that there is a 'public green phone' in the corridor connecting the carriages. Has anyone used or can someone explain how I can make a voice call on that phone. Is it easy to follow instructions? are they in English? do I use coins or need a card?. I will catch the same Shinkansen in November and want to phone friends in Hiroshima to tell them what time I will arrive?. I understand that my mobile from Australia will not work in Japan for making voice calls? . Thank you.

As far as I remember, those green payphones only accept "telephone cards," and these cards (1,000 yen worth) are sold by the card vending machine right next to the phone

Thank you AK, I'll give it a go.