Micro-budget comedy drama Tangerine, the story of two transgender prostitutes in Los Angeles, is remarkable not just because it shows a side of Hollywood rarely portrayed in the cinema, but because the whole film was shot on iPhones.
"All of my films capture street life and are shot clandestinely to a certain degree, but using iPhones on this one helped to even a greater extent," says Sean Baker, director of Tangerine, a breakout hit at this year's Sundance Film Festival.
"It led to a lot of freedom and experimentation. If you had seen us shooting across Santa Monica Boulevard, you would not know we were a professional shoot, except for perhaps our sound gear. "
Instead of using "dolly shots" - with a camera moving on a track - Baker filmed street scenes while riding his bicycle.
UK audiences can see Tangerine when it is released in selected UK cities on Friday alongside big studio offerings such as Steve Jobs, starring Michael Fassbender and Kate Winslet, and The Lady with the Van, with Dame Maggie Smith.
Tangerine, by contrast, features acting newcomers Mya Taylor and Kitana Kiki Rodriguez as trans sex workers on a Christmas Eve odyssey through the streets of LA.
Baker admits he is "pleasantly surprised" at the "universal love" the film has received since its Sundance world premiere in January 2015.
"It's the wonderful personas of the two lead characters who are really pulling audiences in," he says.
"Mya introduced me to Kiki. When I saw the two of them together, I immediately thought 'dynamic duo' - we have to figure out how to get these two on to the big screen."
Inspired by a true story told to him by the actresses, Baker shot the film in the Hollywood neighbourhood where he lived - using three iPhone 5s fitted with special lenses. He treated the footage in post-production to give it a vivid, cinematic sheen.
Sean Baker's tips for filming on a phone
1. Sound quality. If you're going to shoot a feature film on an iPhone, take your sound seriously. Don't skimp on the sound, because that's the first sign of an amateur.
2. Practise. Find the right tools and apps that will help you accomplish what you want. In the last year and a half, tech has advanced to a point where we don't need stabilisers any more - they are all built in to the iPhone 6. I'm jealous of anybody who is shooting stuff today.
3. Take it seriously. Accept it and embrace it and find the benefits that can come from it. I'm sure there are millions of benefits that we didn't even find on our 23 days of filming in 2014. People can use this as tool to experiment and to find different ways of telling stories.
The film's multiple storylines - which also involve a cheating pimp and an Armenian cab driver - converge in a showdown at an all-night doughnut shop.
Because the budget didn't stretch to hiring out the shop for exclusive use, Baker and his cast shot their scenes while the shop was open.
"We had to work round real customers," Baker says. "It actually ended up working in our our favour because it looks a working shop - which it was."
"It could be annoying at times, but it worked," says Mya Taylor.
The actress and singer says she hopes the film will highlight issues affecting the trans community.
"It's hard for us to get a regular job as people automatically discriminate against us," she says.
"Whether you look completely like a girl or not, if they know that you're trans they just don't hire you. I don't have to worry about a regular job any more, but I personally went through that."
Baker regards Tangerine as "one of a million stories" that can be told about the trans communities.
"I hope that films like this that appeal to a greater audience will raise awareness - and then awareness will lead to acceptance," he says.
Taylor says there were two rules she laid down to Baker before filming started.
She says: "I wanted this story to be brutally real and honest and I wanted it to be funny - and he nailed it."
Tangerine is released in the UK on Friday, 13 November