Did you buy Call of Duty 4 for the Xbox 360, PlayStation 3, or PC this week? If so, when you opened the box a little insert may have fluttered to the floor while you were madly slipping the disc into the tray on your system of choice. That slip was an advertisement for Call of Duty 4 on mobile, the first go-go installment of the series handled by Glu Mobile. (Previous editions were released by Hands On Mobile.) A good number of hardcore gamers have likely already dropped the slip in the recycling bin, but to ignore the mobile Call of Duty 4 is to turn your back on a brief bit of engaging entertainment.