Apple's iPhone share of U.S. smartphone subscribers bumped upward 2 percentage points from May through July, giving it 33.4% of the market, online tracking and analytics firm comScore said Tuesday.

The increase could be attributed to broad availability of the iPhone on several U.S. carriers and the availability of more affordable, older iPhone models, including the iPhone 3GS and iPhone 4, as Apple prepares to release a new model, comScore analyst Andrew Lipsman said in an email. Apple is expected to announce a fifth-generation iPhone on Sept. 12.

The iPhone's gain in market share was bigger than Android's improvement of 1.4 percentage points to 52.2% of the market in the U.S. Even so, both platforms are gaining subscribers, Lipsman said.

All other smartphone platforms declined in market share. The BlackBerry from Research in Motion declined by 2.1 percentage points to 9.5% share, and Microsoft's Windows Phone slipped 0.4 percentage points to 3.6%.

There were 114 million U.S. smartphone owners in the three-month period from May through July, an increase of 7% from the period that ended in April, comScore reported.