The iPhone sits in the middle of the headstone and includes a group chat for seven people - Theresa's family.
A number of tributes have been included on the face of the iPhone plaque and have been made to look like text messages received at 12.30pm on Monday, February 3 - the day Theresa was born.
A message from Dad reads: "Thinking of you today, sweetheart, just like I do every day. I miss you and love you my lil angel."
There is also a message from Mum: "The memory of your little hand holding mine brings a warm glow to my heart. I miss you my beautiful daughter."
Theresa has four siblings - Geoffery, Giovanni, Nathaniel and Sieni - who have also sent a message: "Hi Resa, we miss you more than words could explain. Thank you for being best sister / roommate anybody could ask for. Until we meet again. We love you."
'Reach out' - a message to young people
She is also a niece to South Auckland hip hop artist Savage who wrote a song called Reach Out in 2019 in memory of Theresa.
Savage, real name Demetrius Savelio, spoke to the Herald about the heartbreak of losing his niece to a suspected suicide and revealed that he had tried to take his own life at the same age too.
In the music video for the song, featuring young Pacific singing group Tone6, Savage wears a T-shirt with an image of Theresa laughing and the hashtag: #ForTheresa.
"I just want you to know you're not alone. Dig deep. Reach out - and let it out," the rapper says at the start of the clip.
The TikTok video of the headstone has struck a chord with people from around the world; with many expressing their love to Theresa's family.
Some were unsure about the memorial, acknowledging it was a little too different for their liking. But many shared encouraging messages, praising the family's idea for such a unique way of remembering their loved one.
"One of the most unique ones I've seen. May she rest in peace."
A Bible verse is also included on Theresa's headstone: "The Lord is close to the broken hearted and saves those who are crushed in spirit."
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