"He made special mention of 'making suicide' in the City of London and at Heathrow and claimed one of those involved worked at a mosque as a teacher."
Mrs Swain said that during the call Mohidin said: "I've seen some people, they want to make suicide.
"They want to go London and they want to make suicide, you know the president coming tomorrow."
She added: "He said he'd seen a video on how to plant a bomb."
Mrs Swain said it was eventually established a conference was to take place in London, hosted by the prime minister.
"The Somali president and prime minister, and the US Secretary of State Hilary Clinton, were due to attend," she said.
For the next nine hours police sent text messages to Mohidin and arranged to meet him, but he failed to turn up.
In one message he wrote: "Tomorrow is big meeting in London so they will go there and attack."
Mohidin, from Sheffield, was arrested the next day when police found CCTV footage of him topping up the mobile phone used to make the call.
In interview he admitted making the call at 10.47am on February 22, but he denied any references to bombs or suicide attacks.
He told officers he wanted to get the mosque imam into trouble in revenge, because he had caused problems in his marriage.
Alison Dorrell, defending Mohidin, who pleaded guilty to communicating false information with intent, said: "This was a grave piece of conduct and he is very sorry for it. He didn't understand how serious it was."
Jailing him for 18 months, Judge Roger Keen told Mohidin: "You must have known this phone call would cause disruption to the emergency services and potentially to the public.
"It is necessary to protect them from the potential for disruption this type of offending causes.
"Personal mitigation can't save you or anyone else who has done this from immediate custody."