Blackberry:: App. with OS 4.6.xxx and OS 5.0.XXX

i want my App. work with both OS 4.6.xxx(curve 8520) and 5.0.xxx(bold 9000), so in which development environment(JDE versions) i should start to develop it?

Thanks..开发者_JAVA百科

Start with JDE 4.6. Don't use any features of 5.0 and it will run on both OS versions.