App Verify API - Review app best practices

// Requires TargetApi Build.VERSION_CODES.LOLLIPOP_MR1
boolean isVoiceCapabale = telephonyManager.isVoiceCapabale();

## Tell users to omit non-numerals from phone numbers

You should instruct end users to enter their phone number without spaces, dashes, or special characters, because phone number formatting varies by country. Your application should prevent end users from entering their phone number in a formatted way.

## Best practices for phone number formatting
When you pass mobile phone numbers, you must follow strict formatting rules in order for the Telesign server to be able to verify the number. You must normalize the phone number prior to submitting it to the auto verification service.

Telesign accepts phone numbers in the [E.164 format](https://en.wikipedia.org/wiki/E.164), which includes country codes, area codes, and phone number (number string with no spaces, dashes, and so on). For example:

* 13101234567 is normalized from 1(310)123-4567 (United States)
* 447981897555 is normalized from +44-7981-897555 (United Kingdom)

Allow the user to input the phone number.

You must normalize the phone number prior to submitting for processing by doing the following:
* Use regular expressions to strip characters.
* Ensure that there are no characters, such as "," and spaces.

For more information on phone number formatting for Android, see [PhoneNumberUtils](http://developer.android.com/reference/android/telephony/PhoneNumberUtils.html) in the Android Developer Reference.

Telesign recommends that developers allow end users to input the phone number directly in the application. 

## Handling duplicate verification requests
Ensure that a duplicate verification request for the same number is not sent to Telesign for verification when there is an on-going request. For example, the application should not call Telesign API methods to trigger a duplicate verification process. The request should be either a success/failure/timeout which gets returned to the application. You should disable or hide the button which is provided to the end user to trigger the Auto Verification process after the verification process is already triggered. This is to prevent duplicate verification requests originating from the application.

## Tips for cleansing caller ID/CLI

This section provides code samples and information about cleansing an incoming caller ID/Calling Line Identification (CLI) to ensure a greater chance that it will be correctly recognized by your application. 

Telecom providers may add extra digits or characters when sending country code or phone number information. For example, they may prepend +, 0, or 00 to the caller id along with country code that is shown on the mobile phone. They might remove the country code and display only the number, or append additional digits at the end of caller id in rare cases. To handle these situations, do the following: 

1. Sanitize the incoming number by removing any white spaces, special characters, non digits, or leading 0s. You can review the sample code for an example of how you might handle this. 

**Example Caller ID Cleansing Code** 
```java
/***
* Create a sanitized version of a raw phone number using some simple rules:
* Strip any leading characters in the set {'+', '0', '0'}
* Strip out all ' ' characters anywhere in the string.
*
* @param original PhoneNumber The raw phone number retrieved from the runtime or entered * by a User.
* @return The sanitized phone number
*/

String mkSanitizedPhoneNumber(String originalPhoneNumber) {

    try {
        return originalPhoneNumber
                // strip any non digits such as +, whitespace and any other phone number formatting
                .replaceAll("\\D", "")
                // strip any leading 0's
                .replaceFirst("\\A0+", "");

    } catch (Exception e) {
        logger.w(TAG, "Unable to mkSanitizedNumber: ", e);
        return originalPhoneNumber;
    }
}

String parseChallengeCode(String sanitizedPhoneNumber, String prefix) {

    String challengeCode = null;

    if (sanitizedPhoneNumber != null) {

        String pattern = String.format(Locale.US, "\\A(.*)(%s)([0-9a-z]{%s})(.*)\\z",
                prefix, CODE_LENGTH);

        try {
            Pattern r = Pattern.compile(pattern);
            Matcher m = r.matcher(sanitizedPhoneNumber);

            if (m.find()) {
                challengeCode = m.group(3);
            }

        } catch (Exception e) {
            logger.e(TAG, "", e);
        }
    }

    return challengeCode;