Significant differences please. And also, are different versions of android able to use different apps or are all apps available to any android phone. thanks
They are several versions apart. Initially Eclair did not have Flash Support or was capable of WiFi tethering.
No, not every phone running every version of the operating can use any apps. I would imagine an Eclair phone (OS and age) would be quite limited. Also, Ice Cream Sandwich has just come out so it pushes Eclair down even further. Froyo and Gingerbread are the dominant versions of the OS.