Steve Andrews, BT Group chief of mobility and convergence, said on Friday that the offer was one part of the telco's drive to strengthen its virtual mobile operations.
"Anyone who buys BT mobile will get very significantly lower prices on our Wi-Fi," said Andrews.
An official announcement is expected in the next couple of weeks.
BT spun off its mobile operations in 2002 when BT Cellnet became O2, and was floated on the stock market. BT is still keen to be a major player in the mobile space, and on Friday it launched a new range of mobile business services based on Vodafone's mobile network.
This includes a service called the mobile Virtual Private Network. BT says it will mean lower mobile bills for companies as it "enables an employee's mobile device to become an extension of the switchboard".
BT already offered some mobile services through a tie-in with O2, but Friday was the day that it replaced this agreement with its deal with Vodafone. It hopes to be generating £1bn a year from "mobility and convergence revenue" within five years.
BT is also making plans to launch a Wi-Fi phone.
Andrews said that he expected that trial models of a BT Wi-Fi device for enterprise customers would appear "within the window of the next 12 months". He suggested that commercial deployment could be 18 months away.
Such a device would be a second-generation Bluephone -- BT's converged mobile device that is due to launch next year.
Andrews added that there are several problems to be overcome by manufacturers, such as battery life, before Wi-Fi phones are ready for mass-market deployment.