The Android mobile device operating system (OS) from Google Inc. (NASDAQ: GOOG) continues to hold more than half the smartphone OS market, with a 51.7% share for the three-month period ending in April. The iOS platform from Apple Inc. (NASDAQ: AAPL) is the second most popular, with 41.4% market share. But inside the numbers, things look a bit different.

According to Kantar Worldpanel ComTech, Apple’s iOS share is growing faster than Android by a rate of 2.3% growth to 1.4% growth for Android. The bigger news (well, sort of) is that the Windows Phone OS from Microsoft Corp. (NASDAQ: MSFT) is up by 1.8% year over year, even though its overall share remained steady at 5.6%. The three leading operating systems collectively grab 98.7% of the smartphone market. How BlackBerry (NASDAQ: BBRY) hopes to play in this space remains a mystery.

Other interesting data points from the Kantar survey show that Verizon Wireless, a joint venture between Verizon Communications Inc. (NYSE: VZ) and Vodafone PLC (NASDAQ: VOD), is selling more Windows phones and that Sprint Nextel Corp. (NYSE: S) is selling more iOS phones. Verizon’s Windows share rose from 0.2% in April 2012 to 6.8% in April 2013. Sprint’s iOS share grew from 33.4% last year to 38.4% this year.

Some 23% of Windows devices purchasers were former Android device users, while 42% had been feature-phone users. According to Kantar, Apple’s iOS is equally effective at stealing Android users, but it does not match Windows’ appeal to former feature-phone users. Windows phones also gained share in the 25 to 34 year old age group.