Google (Nasdaq: GOOG), the No. 1 search engine, said it has devised a voice-enabled app for Apple (Nasdaq: AAPL) iPhones that will challenge the Siri personal assistant. The move comes two months after Google acquired Motorola Mobility Holdings, one of the top makers of smartphones.

Dubbed "Voice Search" for now, the Mountain View, Calif., company said the service has been made available to developers working on the Android OS for Jelly Bean for a few weeks and will be compliant with Apple's forthcoming iOS version 4.2+.

Like with Siri, a phone user can ask the voice assistant questions such as "How many people live in Cape Cod?" and get an immediate answer from the Google database. The same app will call up lists of movies, restaurants and other materials.

The IPhone app will be available next week in Apple's App Store. Google didn't say when the overall service will be rolled out for Android phones.

Apple, of Cupertino, Calif., has promised to upgrade Siri for new versions of the iPhone anticipated for later 2012 introduction. Earlier, Nuance Communications Inc. (Nasdaq: NUAN), the No. 1 developer of voice-recognition software, announced Nina, a product that sounds like Siri for developers which allows them to work with either iOS or Android systems.

Besides voice enhancements, Google also said it will fine-tune its search functions, so that a user should get a better answer when entering a search term that has different meanings. Entering "Rio," for example, might bring up Rio de Janeiro, a Rio Hotel or a 2011 movie with the same name.

Using the company's Knowledge Graph, a user might also more quickly obtain a listof items such as "California lighthouses."

Meanwhile, Google said gmail users will now be able to sign up to obtain gmail information directly from the search box.

Earlier Thursday, Google agreed to settle privacy infringement charges with the U.S. Federal Trade Commission for a record fine of $25 million. Google said it has cash and investments exceeding $43 billion on June 30.

Google shares rose $1.33 to $643.56 in afternoon trading on Thursday.