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, 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,? she told the judge, Mr Justice Mann.
?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 had never talked publicly about her son?s father, she said.
?This is personal information. It was extremely private.?
Shocked at the story being in the paper and not knowing where the information had come from, she was concerned that her new partner had given the story.
?Obviously, given the evidence I have seen, he hadn?t, but I accused him and our relationship fell by the wayside,? she said.
Ms Gulati said her son ran away from home, aged 11, after another article which said she had been ?dumped? both by her lover and bosses at Coronation Street and might be going into the jungle for I?m A Celebrity? Get Me Out of Here!
?I was in a very unsure position. My mother had also been seriously ill that year and, given I?m a single parent, my son was really concerned who was going to look after him if I was going into the jungle.?
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.
?I was in a very difficult position. I probably left a message begging for him to come back which wasn?t for public consumption. It was between me and him.?
Breaking down in tears briefly, she added: ?It was a very, very difficult time, losing your job as a single parent? when you have no-one to share it with. The one person you share it with is probably your lover at the time? these voicemails were very, very deeply personal.?
She said she continues to be caused ?all sorts of pain and trauma? because she is still unsure ?as to how much of my personal life was listened to by faceless, nameless folk?.
Mirror Group Newspapers last month published an apology for phone hacking, saying the practice was ?unlawful, unacceptable and wrong?.
Ms Gulati said that she regarded a written apology she had received over the hacking at MGN as ?hollow and disingenuous?.
She said she felt relieved when she found out about the hacking as she felt she was going ?barking mad? and had mistrusted everyone.
The newspapers published at least seven stories about Ms Gulati between 2003 and 2006 that were obtained by hacking, the court heard.
Cases from BBC creative director Alan Yentob, soap stars Shane Richie and Lucy Benjamin, former footballer Paul Gascoigne and actress Sadie Frost are also being considered.
TV producer Robert Ashworth, former husband of Coronation Street actress Tracy Shaw, and flight attendant Lauren Alcorn, who was linked to a Premier League footballer, have also brought cases against MGM.
The case continues.