调用系统电话

{  
    //phoneNumber = "18369......"  
    NSMutableString * str=[[NSMutableString alloc] initWithFormat:@"tel:%@",phoneNumber];  
    UIWebView * callWebview = [[UIWebView alloc] init];  
    [callWebview loadRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:str]]];  
    [self.view addSubview:callWebview];  
}