Marketing understands from multiple sources that James has not left BT yet, but has taken a different position within the company's HR department to see out his notice period. He will leave for a competitor in August, likely a mobile company.
BT confirmed James' impending departure, but provided no further details.
It is understood that Ramsay has taken on the role of acting marketing director alongside his usual advertising role. Sources suggest that Ramsay will take on James' duties permanently after the transition period.
David James has been at BT since 2007, and was tasked with turning BT into a credible sports broadcaster. BT Sport now has around five million households signed up, after starting from scratch in August 2013.
James also oversaw the high-profile Adam and Jane campaign, and a more recent parody-style ad featuring Ewan McGregor.
Prior to BT, James held roles at Orange, NatWest and ad agency Rapier.
The news comes one month after group marketing and brand director Suzi Williams announced she would leave BT at the end of the summer. She has been replaced by ex-P&G marketer Zaid Al-Qassab.