NIAgendaDetailViewController.m

// the long text that needs to fit in the label
static NSString *longText = @"Lorem ipsum dolor sit amet, consectetur adipiscing elit. Vestibulum aliquet ornare quam vitae pulvinar. Vestibulum dapibus posuere facilisis. Maecenas iaculis nibh eu felis accumsan, id blandit metus congue!!!";

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    if (indexPath.row == 0) {
        NIAgendaDetailMainCell *cell = [tableView dequeueReusableCellWithIdentifier:@"agendaDetailMainCell" forIndexPath:indexPath];
        cell.lblNotes.text = longText;
        return cell;
    } else {
        // generate the other cells
    }
}

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
{
    if (indexPath.row == 0) {
        self.mainCellTemplate.lblNotes.text = longText;
        CGSize size = [self.mainCellTemplate.contentView systemLayoutSizeFittingSize:UILayoutFittingCompressedSize];
        CGFloat calculatedHeight = size.height;
        return calculatedHeight;
    } else {
        // return the static height of the other cells (44)
    }
}