you should be aware that the prompt will only be displayed to a user a maximum of three times within a 365-day period. Choosing when and where to display this prompt is critical to your success using this API.
If you want to always ask the user for a review (a bad idea IMHO) you can write your own UIWebView method that does something like:
[myWebView loadRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:@"itms-apps://itunes.apple.com/app/idYour Apple ID?mt=7"]]];
>Can you have the possibility to open prompt every time in my app?
Recommend you read/follow what the HIGs say about that...