Operating system have developed a lot in last 15 years. Starting from black and white phones to recent smartphones or mini computers, mobile OS has come far away. One of the most widely used mobile OS these days is ANDROID. Android is a software bunch comprising not only operating system but also middleware and key applications. After original release there have been number of updates in the original version of Android. It is the software stack of mobile devices. Android SDK provides the API's that is necessary to begin developing applications on the Android platform using the Java programming language. Android includes an embeddable browser built upon WebKit, the same open source browser engine powering the iPhone's Mobile Safari browser. An Android application consists of one or more of the following classifications: 1)Activities: Is the application that has a visible UI is implemented with an activity. When a we selects an application from the home screen or application launcher, an activity is started.2)Services: A service should be used for any application that needs to persist for a long time, such as a network monitor or update-checking application. 3)Content providers: We A content provider's job is to manage access to persisted data, such as a SQLite database. Suppose for the bigger system like Speech to text conversion system or one that makes data available to multiple activities or applications, a content provider is the means of accessing your data.4)Broadcast receivers: This is use to launched to process a element of data or respond to an event, such as the receipt of a text message. Following figure showing the Architecture of Android platform. The key application of the speech to text conversion system is recognition technology. Speech input adds another dimension to the mobile phones. The Google's Voice Search application, the is required is many times pre-installed on many Android devices and available in Android Market, and it provides powerful features. Now we can dictate our message instead of typing it. Just tap the new microphone button on the keyboard, and you can speak in just about any context in which you would normally type.