BT is expected to announce its return to the UK mobile sector this week, by launching its own 4G network.
The broadband provider - which sold mobile network O2 to Telefónica in 2005 - has long been planning a return to the industry as it gears up to introduce quad-play bundles.
With BT's takeover of mobile operator EE ongoing, the firm is planning to introduce mobile voice, SMS and broadband services under its own branding.
The Financial Times says existing customers will be able to sign up for inexpensive mobile deals to complement fixed-line broadband, TV and home phone.
The new service - which is expected to be called BT Mobile - will use EE's network under a wholesale agreement signed in 2014.
It will enable BT customers to sign up for mobile services before the company's intended acquisition of EE receives regulatory approval.
The news provider says BT will not give away mobile services to existing customers in the same way it has with BT Sport.
The pay-TV service has been free online to BT customers during its first two years on UK TV screens.