Amazon appears to be giving Netflix a hard run for the money as it adds subscribers to its Amazon Prime Instant Video service. In a conference call with reporters and analysts on Tuesday, Amazon CFO Tom Szkutak said that the number of customers who are using their Amazon Prime subscription service to view movies and TV episodes has gone up dramatically year-over-year. Originally, the Amazon Prime service provided unlimited free shipping to customers for a flat monthly fee that is comparable to Netflix's subscription fee for online video. It now also includes on-demand access to 36,000 movies and television episodes. You should expect that we will be spending more on content on Prime over time, Szkutak said. The company also said that its digital media selection of movies, TV shows, recordings, books, etc. grew to more than 23 million from 19 million a year ago. Amazon's share were up nearly 10 percent in after-hours trading on Tuesday but were up around 6 percent at midday today (Wednesday).