How to make sure an Android App works on most smartphones?

How can i make sure that my android app works on majority of the devices in the market. What testing tools do i have to use? Obviously if there are 12 or more smartphones in the market then i cannot buy each of them to test my app.So what shoul开发者_如何学Pythond i do? Wonder if "Dvice Anywhere"(http://www.deviceanywhere.com/) can help us in this regard?

Does firmware or OS version also matters (1.5,1.6, 2.0, etc.)?

Please comment and explain.