Samsung claims the foundation for the design of the iPhone began with a 2006 Businessweek interview with Sony designers Takashi Ashida and Yujin Morisawa. The article was passed from Apple SVP Tony Fadell to Steve Jobs and Jony Ive.
Here's Samsung's description of the story:
Right after this article was circulated internally, Apple industrial designer Shin Nishibori was directed to prepare a "Sony-like" design for an Apple phone and then had CAD drawings and a three-dimensional model prepared. Confirming the origin of the design, these internal Apple CAD drawings prepared at Mr. Nishibori's direction even had the "Sony" name prominently emblazoned on the phone design, as the below images from Apple's internal documents show:
Soon afterward, on March 8, 2006, Apple designer Richard Howarth reported that, in contrast to another internal design that was then under consideration, Mr. Nishibori's "Sony-style" design enabled "a much smaller-looking product with a much nicer shape to have next to your ear and in your pocket" and had greater "size and shape/comfort benefits." As Mr. Nishibori has confirmed in deposition testimony, this "Sony-style" design he prepared changed the course of the project that yielded the final iPhone design.
Notably, Samsung's argument is actually based on Morisawa's response to the question, "How much did the iPod influence your design?"
"The idea was to do away with excessive ornamentation. I looked at the first Walkman [which debuted in 1979]. Then I thought, "How can I give shape to the music?" Music doesn't have shape; it's flowing. I was listening to music and waving my hand in the air. I thought there shouldn't be an end to its lines. So I started drawing a round shape, and I kept moving the line. My team had shown me their sketch: It was a square with a screen and buttons. Most other players have a screen and buttons. My first mock-up didn't have buttons. I didn't want buttons."
While this is likely not enough to convince anyone that Apple copied a Sony design, it could weaken Apple's argument that Samsung 'slavishly copied' the iPhone. If the iPhone's design is largely inspired by a Sony design than Apple can't accuse Samsung of copying.
"Samsung has used the very same public domain design concepts that Apple borrowed from other competitors, including Sony, to develop the iPhone," argued Samsung.