1.
NSMutableString* str=[[NSMutableStringalloc]initWithFormat:@"telprompt://%@",@"400****688"];
[[UIApplicationsharedApplication]openURL:[NSURLURLWithString:str]];
2.
NSMutableString* str=[[NSMutableStringalloc]initWithFormat:@"tel:%@",@"400****688"];
UIWebView* callWebview = [[UIWebViewalloc]init];
[callWebviewloadRequest:[NSURLRequestrequestWithURL:[NSURLURLWithString:str]]];
[self.viewaddSubview:callWebview];