public class PhoneDialerTest
{
    public async Task PlacePhoneCall(string number)
    {
        try
        {
            PhoneDialer.Open(number);
        }
        catch (ArgumentNullException anEx)
        {
            // Number was null or white space
        }
        catch (FeatureNotSupportedException ex)
        {
            // Phone Dialer is not supported on this device.
        }
        catch (Exception ex)
        {
            // Other error has occurred.
        }
    }
}