Hi,

Can we program any application as common .So it supports all Android mobile devices.If it so ?Please say me how?

Mostly. Aim for 1.5 and you'll cover the vast majority of devices. I read an article claiming that within a year, over 80% of the devices will be on 2.1 or higher, so aiming for 2.1 might not be bad either, especially if you're expecting a lengthy development cycle.