Sending USSD code with alphabetic characters

In my android app, I am sending USSD codes (#144#73#) using below Intent :

String baseUssd = Uri.encode("#") + "144" + Uri.encode("#");
StringBuilder builder = new StringBuilder();
builder.append(baseUssd);
builder.append("73");
builder.append(Uri.encode("#"));

Intent intent = new Intent(Intent.ACTION_CALL, Uri.parse("tel:" + builder.toString()));

It's working well.

What I want now is to send this code :

#144#73MA#

I run this using the dial pad, following the Operator USSD menu, that worked. But if I try to do this programmatically using the above Intent that didn't work.

I know that alphabetic characters can't be used when typing code with the Dial Pad, but I though that It can be possible programmatically !!

Any Idea please !

Edit

When I try to send this programmatically : #144#73MA# I noticed that the Dialer application changes the alphabetic characters to their corresponding digit in the dial pad. Meaning that the dialer transform this : #144#73MA#

to this #144#7362# : why ?

Because :

the M matches the digit 6
the A matches the digit 2

Meaning that the dialer transform this : #144#73MA#

to this #144#7362# : why ?

I will try to answer only the why part.

Intent.ACTION_CALL is handled by OutgoingCallBroadcaster class. If you look at processIntent() method, there is this piece of code (lines 438~448 as of this writing):

String number = PhoneNumberUtils.getNumberFromIntent(intent, this);
// Check the number, don't convert for sip uri
// TODO put uriNumber under PhoneNumberUtils
if (number != null) {
    if (!PhoneNumberUtils.isUriNumber(number)) {
        number = PhoneNumberUtils.convertKeypadLettersToDigits(number);
        number = PhoneNumberUtils.stripSeparators(number);
    }
} else {
    Log.w(TAG, "The number obtained from Intent is null.");
}

There PhoneNumberUtils.convertKeypadLettersToDigits() converts the letters into the equivalent numeric digits:

public static String convertKeypadLettersToDigits (String input)

Translates any alphabetic letters (i.e. [A-Za-z]) in the specified phone number into the equivalent numeric digits, according to the phone keypad letter mapping described in ITU E.161 and ISO/IEC 9995-8.

Returns
the input string, with alpha letters converted to numeric digits using the phone keypad letter mapping. For example, an input of "1-800-GOOG-411" will return "1-800-4664-411".

Hope this helps.