How to display 2 lines of text for subtitle of MKAnnotation and change the image for the button on the right?

- (MKAnnotationView *)mapView:(MKMapView *)mapView viewForAnnotation:(id <MKAnnotation>)annotation
{   
    MKAnnotationView *annotationView = [[MKPinAnnotationView alloc] initWithAnnotation:annotation reuseIdentifier:@"loc"];

    // Button
    UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
button.frame = CGRectMake(0, 0, 23, 23);
button.contentVerticalAlignment = UIControlContentVerticalAlignmentCenter;
button.contentHorizontalAlignment = UIControlContentHorizontalAlignmentCenter;

[button setImage:[UIImage imageNamed:yourImageName] forState:UIControlStateNormal];
[advertButton addTarget:self action:@selector(buttonPress:) forControlEvents:UIControlEventTouchUpInside];

annView.rightCalloutAccessoryView = button;


    // Image and two labels
    UIView *leftCAV = [[UIView alloc] initWithFrame:CGRectMake(0,0,23,23)];
    [leftCAV addSubview : yourImageView];
    [leftCAV addSubview : yourFirstLabel];
    [leftCAV addSubview : yourSecondLabel];
    annotationView.leftCalloutAccessoryView = leftCAV;

    annotationView.canShowCallout = YES;

    return pin;
}

UPDATE

The default style for annotations only supports the title and subtitle. Neither title nor subtitle can include line breaks. You cannot do this without subclassing.

To use a custom view review Apple's sample code:

http://developer.apple.com/library/ios/#samplecode/WeatherMap/Introduction/Intro.html

I also think there is a problem in your code

UILabel *l1=[[UILabel alloc] init];
l1.frame=CGRectMake(0, 15, 50, 50);
l1.text=@"First line of subtitle"; 
l1.font=[UIFont fontWithName:@"Arial Rounded MT Bold" size:(10.0)];

UILabel *l2=[[UILabel alloc] init];
l2.frame=CGRectMake(0, 30, 50, 50);
l2.text=@"Second line of subtitle";
l2.font=[UIFont fontWithName:@"Arial Rounded MT Bold" size:(10.0)];
[leftCAV addSubview : l1];
[leftCAV addSubview : l2];

l1 has a frame (0, 15, 50, 50) and l2 has (0, 30, 50, 50). Wont these two overlap? I mean l1 will start from y=15 and its height is 50. so when l2 starts from 30 it may overlap.. Can you pls check by changing the frames

plz use this

 - (MKAnnotationView *) mapView:(MKMapView *)mapView viewForAnnotation:(id<MKAnnotation>)annotation {

        if ([annotation isKindOfClass:[MKUserLocation class]])
            return nil;
        if ([annotation isKindOfClass:[CustomAnnotation class]]) {
            CustomAnnotation *customAnnotation = (CustomAnnotation *) annotation;

            MKAnnotationView *annotationView = [mapView dequeueReusableAnnotationViewWithIdentifier:@"CustomAnnotation"];

            if (annotationView == nil)
                annotationView = customAnnotation.annotationView;
            else
                annotationView.annotation = annotation;

            //Adding multiline subtitle code 

            UILabel *subTitlelbl = [[UILabel alloc]init];
            subTitlelbl.text = @"sri ganganagar this is my home twon.sri ganganagar this is my home twon.sri ganganagar this is my home twon.  ";

            annotationView.detailCalloutAccessoryView = subTitlelbl;

            NSLayoutConstraint *width = [NSLayoutConstraint constraintWithItem:subTitlelbl attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationLessThanOrEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1 constant:150];

             NSLayoutConstraint *height = [NSLayoutConstraint constraintWithItem:subTitlelbl attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationGreaterThanOrEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1 constant:0];
            [subTitlelbl setNumberOfLines:0];
            [subTitlelbl addConstraint:width];
            [subTitlelbl addConstraint:height];




            return annotationView;
        } else
            return nil;
    }

This is how I achieved it without subclassing the annotation view, or using undocumented APIs:

MKAnnotationView* pinView = (MKAnnotationView*)[mapView dequeueReusableAnnotationViewWithIdentifier:@"CustomPinAnnotationView"];

// Add a custom view to the the callout to allow mutli-line text
UIView *calloutView = [[UIView alloc] initWithFrame:CGRectMake(0, 10, 250, 250)];
UIView *calloutViewHeight = [[UIView alloc] initWithFrame:CGRectMake(0, 10, 1, 250)]; // The reason for this will become apparent below
UILabel *title = [[UILabel alloc] initWithFrame:CGRectMake(10, 10, 250, 21)];
[title setText:<<your single-line title text>>];
[calloutView addSubview:title];
UILabel *subtitle = [[UILabel alloc] initWithFrame:CGRectMake(10, 35, 250, 250)];
[subtitle setNumberOfLines:0];
[subtitle setText:<<your multi-line title text>>];
CGSize subtitleSize = [subtitle sizeThatFits:CGSizeMake(250, 250)];
[subtitle setFrame:CGRectMake(10, 35, 250, subtitleSize.height)];
[calloutView addSubview:subtitle];
[calloutView setFrame:CGRectMake(0, 10, 250, 35+subtitleSize.height+10)];
[calloutViewHeight setFrame:CGRectMake(0, 0, 1, 35+subtitleSize.height+10)];
pinView.leftCalloutAccessoryView = calloutView;
pinView.rightCalloutAccessoryView = calloutViewHeight;  // The height of the callout is calculated by the right accessory *not* the left, so this fake view is required

You can customize the font/color of the text by adjusting title and subtitle accordingly.

Sure it's a bit of a hack, but it achieves the desired results without subclassing, and allows you to customize with whatever additional buttons/images you'd like to add calloutView (and you can still place buttons in the right-accessory view if you wish, as long as you retain the height).