According to officials, 44-year-old Argishti Khudaverdyan of Burbank fraudulently unlocked and unblocked cellphones on T-Mobile's network, along with Sprint, AT&T and other carriers.
He was found guilty Friday after a four-day trial.
The Justice Department said he would get unauthorized access to T-Mobile's internal computers by using employees' credentials through "various dishonest means," including sending emails and hacking the T-Mobile IT Help Desk.
Khudaverdyan stole more than 50 different T-Mobile employees' credentials from workers across the U.S., the Justice Department said.
Officials said he used the $25 million to buy property in Burbank and Northridge.
He was found guilty of one count of conspiracy to commit wire fraud, three counts of wire fraud, two counts of accessing a computer to defraud and obtain value, one count of intentionally accessing a computer without authorization to obtain information, one count of conspiracy to commit money laundering, five counts of money laundering, and one count of aggravated identity theft.
Khudaverdyan is scheduled to be sentenced on Monday, Oct. 17.
The 44-year-old could get at least two years in prison for the aggravated identity theft charge.
He could also get up to 165 years for counts relating to wire fraud, money laundering and accessing a computer without authorization.