Jan 11 (Reuters) - Apple Inc asked for $1 billion as an "incentive payment" from Qualcomm Inc in order for Qualcomm to become the supplier of modem chips for Apple's iPhone, Qualcomm's chief executive testified on Friday at a trial with U.S. antitrust regulators.

The $1 billion payment as part of a 2011 deal between Apple and Qualcomm was meant to ease the technical costs of swapping out the iPhone's then-current chip with Qualcomm's.

But Qualcomm CEO Steve Mollenkopf testified at a trial with the U.S. Federal Trade Commission that the hefty payment was part of why Qualcomm sought to become the sole supplier of Apple's so-called modem chips. (Reporting by Stephen Nellis; Editing by Sandra Maler)