The hacked voicemails were "deeply personal", she told the High Court. She had accused her partner of leaking information, causing their relationship to fall "by the wayside", she said.
Ms Gulati, pictured, who played Sunita Alahan in the drama, is among eight high-profile figures claiming damages for hacking.
The actress told the court her phone started to be hacked from 2003, two years after she joined the ITV soap opera.
At one point she wrote to the Press Complaints Commission after an article appeared in the Sunday Mirror about her "secret marriage", she said.
She said the "salacious gossip" about her past led to her son being bullied "quite extensively" the following day at school about who his father was.
"I'm a single mum living on my own with my son. I believed it wasn't in the public interest that the parentage of my child would be debated in a Sunday newspaper, so I wrote this letter. I've always been very careful about answering questions about my son and had never been photographed with him until he was 18," she told the judge, Mr Justice Mann.
She had never talked publicly about her son's father, she said.
"This is personal information. It was extremely private."
The 48-year-old actress, who is currently appearing in Mamma Mia in Liverpool, said she had never been offered the reality show, but humorously referred to the possibility on voicemails she left.
She said she had not spoken publicly about her disappointment over leaving Coronation Street, but had on voicemail. Nor had she spoken out about the end of her relationship - although she left many voicemails for her boyfriend, she said.
The case continues.
