app compatiblity on iphone

i am new to iphone apps development.i want to develop Iphone applicaiton.which version i need to use and that should support run older and new versi开发者_Go百科on of Iphone.

which device is best for testing apps like 2g,3g,3gs

Thanks in advance

Aswan

It depends on the application. I am focused on games, so my target devices are 3G and iPod Touch (not the new one). Something older may be quite too restrictive for some ideas... At some point I will switch to the new 'retina display' models. But not now: the cake is still way too big with the not-so-old models!

Nevertheless, Apple forces you to use the latest XCode (4.1 devices). However, while you are forced to use the latest SDK, you may still target older devices (3.0 in our case, for example). You may go back to 2.1.1 devices, if I remember well.

Good luck!