Usage of Apple’s iPhone slid more than 4 percent in December despite what analysts estimate will have been a huge month in Apple’s biggest-ever quarter of sales. Advertising network Chitika on Friday published its smartphone vendor usage share data for the month of December as measured by traffic across its network. Apple’s iPhone showed the biggest slide last month but Apple was still the most popular vendor by a wide margin with a 49.62% share. Chitika also recently reported that iOS’s overall operating system share was up 1.12% in December. HTC’s vendor share followed at 16.83%, up 1% from November, and Samsung jumped 2.74% to 14.53% in the No.3 spot. Motorola was nearly flat at 7.94% and RIM slid half a point to 0.99%.