She said her brother went to take classes today at the civic association and that she had not heard from him since. She said she did not know that he was involved in the shooting.
"I'm going to pass out," she said, and she hung up the phone.
A neighbor who lived on the same block as Voong and his family described the family as "quiet" and said they mostly kept to themselves.
"They were nice people," said the neighbor who identified herself only as Darlene. "They were good neighbors."
Police also contacted Voong's sister to say her brother was dead. She told police that Voong was attending language classes at the civic center. She said Voong is a U.S. citizen and has been in this country for 28 years.
U.S. Rep. Maurice Hinchey, a Democrat whose district includes Binghamton, initially told the Associated Press Voong was recently laid off from IBM in Johnson City -- but sources later told ABC News that it appeared that the Voong who worked at IBM was Henry Voong, "an older gentleman" who was believed to be the suspect's father, and that he had not been laid off.
Fred McNeese, an IBM spokesperson, said that because the police have not officially identified the shooter, the company is "unable to confirm any connection to IBM" at this time and has no other comment.
Several hours after the shooting began, hostages started exiting the building and police declared the gunman dead.
By 1:30 p.m., police began escorting people out of the building, but continued to treat the building as a crime scene where the shooter might still be lurking.
The American Civic Association released a statement early Saturday morning.
"We are stricken with grief about today's horrific assault and share this grief with the victims' families, our community and the entire nation."
Eyewitness Nick Masucci, a community college student and Binghamton resident, said he watched as many as 20 people exit the building and get patted down by police.
"They look like immigrants, lots of different cultures coming out of there. Some people are getting patted down. The police are taking a lot of precautions, they're still taking cover," he said.
Several people were removed from the building on stretchers. Others left with their hands on their heads and were searched by police.
Earlier today, police called Broome Community College to find someone who could speak fluent Vietnamese to "assist police with translation," said college spokesman Richard David.
People were told in nearby buildings to stay away from windows and Binghamton High School is under a lockdown as police use the school as a staging area. The school is a block and a half away from the shooting site.
President Obama issued a statement from the NATO summit he was attending in France.
"Michelle and I were shocked and deeply saddened to learn about the act of senseless violence in Binghamton, N.Y., today. Our thoughts and prayers go out to the victims, their families and the people of Binghamton," he said.
New York Gov. David Paterson called the shooting "the worst tragedy and senseless crime in the history of the city."
"We all just have profound sorrow and sadness," he said.
Additonal reporting by ABC News' Ned Potter and Ki Mae Heussner.