Sister Wolfgram can only see her family twice a year via Skype: on Mother's Day, and at Christmas.

She's allowed to email relatives weekly, but as a Mormon missionary, this is the most contact will she have with her family, during her 18 months of overseas service.

"I come from a family of 10, there's four brothers and four sisters, so I miss them a lot," says Sister Wolfgram, who was raised in West Valley City, Utah, a majority Mormon state.

Her family is originally from Tonga, another heartland for the Church of Jesus Christ of Latter-day Saints — home to more Mormons per capita than any country in the world. Statistics show that nearly 60 per cent of the population belongs to the church.

"As Tongans, the two most important things are God and family … and then food," Sister Wolfgram smiles.

She is one of the 80,000 voluntary missionaries currently serving an 18 to 24-month placement assigned and organised by the church and, like all female missionaries, she's given the title 'sister'.

Male missionaries are called 'elder', regardless of age.

The sisters scout for people who may be willing to talk. ( ABC RN: Siobhan Hegarty )

Modern-day evangelists

Today, Sister Wolfgram is preparing to go 'street contacting' with fellow missionary Sister Lu.

It's her fourth day working in the Sydney CBD a YSA ward, which means she's focused on serving young single adults, aged 18 to 30 years. It's quite a shift from her last posting in suburban Castle Hill, where 'door knocking' is the preferred method of making contact.

"Door knocking is a bit easier because you have them then and there; they can't run anywhere else except slam the door," Sister Wolfgram laughs.

And does that happen often?

"[There's] plenty and plenty of those experiences, and it's all just a matter of not taking it personally, just moving on," she smiles.

Her companion Sister Lu is — unexpectedly — a natural at talking to strangers.

With her soft accented voice, little more than a whisper, Sister Lu takes passers-by off guard with her gentle approach to proselytising — if you could call it proselytising at all.

The sisters carry Mormon pamphlets in various languages for foreigners. ( ABC RN: Siobhan Hegarty )

Leaving the church's Hyde Park Chapel, the sisters immediately spot a young man standing idly on the street.

They wonder out loud whether he's waiting for a taxi, then decide to approach.

The exchange lasts no more than five minutes, but finishes with a phone number swap and a hushed prayer.

Afterwards, Sister Wolfgram reflects on their conversation: "Honestly, he was like, 'Wait, what is going on?' but when we come with a soft approach, like 'Oh we're volunteer teachers …' and we introduce what we do as missionaries, it kind of sparks that interest."

"He's a Buddhist," interjects Sister Lu.

"So, he hasn't prayed before and he doesn't speak English well.

"He's from Thailand and we have a pamphlet in Thai, so we open that page explaining how we pray and why we pray.

"We asked him if we can pray for him because he works in a Thai restaurant, and he works very hard and he's tired — so we pray for him and he felt nice."

To enable the continuation of street conversations, the sisters hand out business cards with their missionary mobile number, and ask for the digits of the person they've just interacted with.

If successful, they'll call the interested party and set up a meeting to speak more about the Book of Mormon and the values of their church.

Sister Lu prefers 'street contacting' over door-knocking to spread the word of the Church. ( ABC RN: Siobhan Hegarty )

A religious awakening

Unlike Sister Wolfgram, who grew up in a Mormon household, Sister Lu entered the faith two years ago.

"My dad's family is Taoist and my mum's family is Buddhist, so I grew up believing a kind of like a mixed religion [which] is really common in Taiwan," she says.

Despite her family's religious convictions, Sister Lu spent her teenage years questioning her life's purpose. She sought guidance from a Buddhist monk, but was left feeling disconnected and lost.

It wasn't until a couple of Mormon missionaries approached her in the street that Sister Lu discovered her faith in God.

"They changed my life and my view of the world, so that's why I chose to be baptised and I wanted to be a missionary like them," she says.

"I know there are a lot of people like me who [don't] know who Jesus Christ is, so we get to find those people and help them know more about that."

It's somewhat of an art identifying passers-by who might be willing to converse about Jesus Christ, but Sister Lu — who has a nose for it — quickly teaches Sister Wolfgram the ropes.

"People in the city, they are busy for work or study, and sometimes they are lonely, especially international students," she points out.

"Sometimes they don't have family or friends, so they sometimes really like going to church because they feel [loved] there."

The Book of Mormon effect

Sister Lu says occasionally she spots people who look like they're in need of the missionary message, so she'll run over to stop them and start a conversation.

But thanks to a certain Broadway musical currently playing in Australia, the lines of communication are beginning to go both ways.

Cast of the Book of Mormon take to the stage in Melbourne for the premiere. ( Supplied )

According to the church's public affairs director Chris Stuart, the Book of Mormon musical — which played in Melbourne last year and opened in Sydney on Wednesday — has increased the general public's interest in the faith.

"For the missionaries … they've had people coming up to them [asking], 'Tell us about what you believe. Tell us about the Book of Mormon. Can we have a copy of the Book of Mormon?'" he says.

The musical, written by the creators of South Park, follows two Mormon missionaries trying to spread the word of the Mormon faith to a fictional tribe in Uganda.

Despite the production's satirical skewering of the religion, Mr Stuart says the church, which now has more than 15.8 million members, has benefited from its success.

"You would think because of how the church is portrayed, and how missionaries are portrayed, perhaps it'd be a negative, but that definitely hasn't been the case," he says.

Mr Stuart notes the church even tried to purchase an advert in the Melbourne musical's programme — as was done in cities overseas — but their request was denied.

"When the play was in London they took advertising in the leaflet, and it was something about, 'You've seen the play, read the book — the book's always better'," he recalls.

A new Mormon missionary arriving in Sydney. ( ABC RN: Siobhan Hegarty )

While Sister Wolfgram and Sister Lu haven't seen the musical, they wholeheartedly agree that the actual Book of Mormon is better than any sardonic spin-off.

And their weekly email session is full of laughs, anyway.

"When I'm talking with my best friend who's serving in Zimbabwe, he's like, 'Oh no big deal, just running away from lions', and I'm like, 'Oh, that's great, I'm just running after a bus!'" she giggles.

"So it's definitely different cultures and environments wherever we go. Nevertheless, the gospel is still the same that we share."