I have iPhone 4 device and tested my app on it and it works perfectly fine, but when I sent app to my client having iPhone 3GS, its crashes at some particular view.
My question is that can I test my app on 3GS without real device like on simulator?,Also am I able to see the crash device logs of my client device.
First you have to get the crashlog from your client, as it was probably you who compiled the build, your XCode will be able to symbolicate it. Then it should be easy to find the line wich crashs.
You can also try to reproduce the crash with the emulator, but keep it mind that it's not exactly the same as a real device, So, it may work on the emulator and not on a real device.
You can have the logs like that : http://www.iphonedevsdk.com/forum/iphone-sdk-development/55116-how-get-crash-logs-data-iphone-os-ios.html
Ask your client to do so.