Mobile advertising may be a growing business, but smartphones may have reached peak market share according to Millennial Media’s latest quarterly Mobile Mix report. The mobile advertising company found that smartphones accounted for 74 percent of all impressions served on its network during Q2 — up just one percent from Q1′s 73 percent.

Although Millennial found the share of smartphone impressions served to overall impressions was stagnant quarter-over-quarter, year-over-year smartphone impressions have risen by eight percent.  The lack of growth in smartphone impressions is likely due to the stabilization of feature phone impression share. Millennial found that feature phones accounted for seven percent of all impressions it served during Q2 2012, the same amount they accounted for in Q1 2012. The report marks the the first time in over a year that feature phone impressions haven’t dropped quarter-over-quarter. For reference, at this time last year feature phones accounted for 17 percent of all impressions served through Millennial’s advertising platform.

Non-phone connected devices — a category which includes tablets, e-readers and MP3 players such as the iPod Touch — dropped one percent quarter-over-quarter to 19 percent, but were up two percent year-over-year.

According to the mobile advertising company, the top five tablets on its platform by impressions for Q2 2012 were the iPad, Samsung Galaxy Tab, Amazon’s Kindle Fire, the Acer Iconia, and the Motorola Xoom. The Acer Iconia bumped the BlackBerry Playbook out of its top five spot from last quarter. Apple’s iPad, Samsung’s Galaxy Tab and Amazon’s Kindle Fire once again ranked in the top 20 mobile devices by impressions served. The Galaxy Tab remained the top Android tablet but the new line of Kindle Fires could give the Galaxy Tab some competition over the coming holiday season.

Apple remained the No. 1 manufacturer by devices on Millennial’s list, accounting 31.3 percent of overall impressions served — up from 28.3 percent in Q1 2012. Samsung was the No. 2 OEM with 21.9 percent of all impressions. Combined, Apple and Samsung devices account for more than 50 percent of the impressions Millennial serves through its advertising platform. Once again Apple’s suite of iPhone handsets were the most popular type of device Millennial tracked, accounting for 15.8 percent of impressions in Q2, up from 15.1 percent last quarter. The second most popular device the company tracked was the BlackBerry Curve, which saw 4.96 percent of all impressions Millennial served in Q2 2012.