The iPhone 4S lifted Apple‘s (NASDAQ:AAPL) fortunes with the stock now hovering at an all-time high price of $520 from around $400 in October last year when the iPhone 4S was launched. Not only has the iPhone 4S helped Apple become the number one global smartphone player, but it has also helped narrow the gap with Google’s (NASDAQ:GOOG) Android operating system in the U.S. in the last quarter.
According to a report, during the October 2011 to January 2012 period, Apple led the mobile ad impressions market in North America with a share of 35%.  Clearly, the launch of iPhone 4S helped Apple surpass Android while Research in Motion’s (NASDAQ:RIMM) BlackBerry operating system saw an even steeper decline than Android dropping 8.9% to finish at third place with 11.6% share during the same period.
Our $550 price estimate for Apple’s stock is about 5% above the current market price.
Mobile usage directly depends on smartphone popularity
Apple’s growth in mobile ad impressions market is a direct result of iPhone’s increasing popularity. According to one report, iPhone 4S, iPhone 4 and iPhone 3GS took the top three spots in the U.S. smartphone market last quarter, and iOS, with a market share of 43%, narrowed the gap with Android at 48% in the smartphone operating system market. 
Even globally, Apple is now the leading smartphone player. It recently overtook Samsung to gain the number one spot with a market share of 24% in Q4 2011.  This goes to show that more popular the smartphone, higher is the mobile web and apps usage. The increase in this usage results in increased mobile ad impressions.Notes:
- Apple’s iOS passes Android, accounts for 35% of mobile ad impressions, AppleInsider quoting InMobi, the largest independent mobile advertising network, as the source, February 24th, 2012 [↩]
- The NPD Group: Apple Leads Mobile Handsets in Q4 2011, but Android Attracts More First-Time Smartphone Buyers, February 6th, 2012 [↩]
- Apple Becomes World’s Largest Smartphone Vendor in Q4 2011, Strategy Analytics, January 26th, 2012 [↩]