By Trefis.comNEW YORK ( TheStreet) -- Apple ( AAPL) recently announced that it sold 1 million iPads within the first 28 days after the April 3, 2010 launch of the device in the U.S. In comparison, it took 74 days for Apple to sell one million iPhones in 2007 and Amazon ( AMZN) sold only about 1 million Kindle e-reader devices in total throughout all of 2009. Furthermore, the new iPad 3G is off to a good start, having sold an estimated 300,000 units over the weekend of April 30. Based on the strong demand for the iPad thus far and the fact that the holiday season for 2010 could trigger an even bigger response, iPad unit sales may exceed our forecast of 4 million iPads sold in 2010. We estimate that the iPad constitutes 4% of the $294 Trefis price estimate for Apple's stock and that there could be an additional 3% upside to our Apple estimate if iPad unit sales were to exceed our forecast by reaching as high as 10 million units by the end of 2010. Even if Apple were to sell 10 million iPads in 2010 and about 24 million by the end of forecast period, our Apple estimate would not exceed $310. iPad Sales to Reach 4 Million Units in 2010 We currently forecast that iPad sales will reach 4 million units sold in 2010. In comparison, we forecast that Amazon will sell only 2 million Kindles in 2010. Apple sold about 3.7 million iPhones in 2007 after launching the device in June of that year and it subsequently sold nearly 14 million iPhones during 2008. Given the strong performance of iPad sales and the past performance of iPhone sales, you can modify our forecast above to see how Apple's stock could be impacted if iPad sales were to exceed our forecasts.