Gearbox Software, the developer of big games like Borderlands 2, received an offer from Activision to make a Call of Duty game, at least according to a supposed interview with the studio's president, Randy Pitchford.
Gearbox is an independent developer that has worked with many different publishers on many different games. From the Borderlands series with 2K, to the Brothers in Arms one with Ubisoft or the upcoming Aliens: Colonial Marines with Sega.
The offer, however, was turned down, as Gearbox was supposed to create a game based on Activision's rules and not bring anything completely new to the table.
These restrictions didn't make sense for Pitchford and his team so Gearbox didn't work on Call of Duty, instead choosing to focus on its own projects.