Java program to auto dial a calling card phone number, issues with entering card number

I wrote a Java program to mimic the sounds to dial phone numbers, it works fine except when it comes to phone cards, it needs to dial a local number first (no problem, it successfully connects to a local number), then it needs to enter the card number, problem is the开发者_如何学Python other end won't accept the generated sounds for the card numbers, it only takes hand entered card numbers (I had to physically enter the digits on the phone keypad by hand), why can it take phone number by sounds while not being able to take sounds for the card numbers ? Anyone familiar with the phone system can answer this question ? Anything I can do so my Java program will be able to mimic the entering of the card numbers ?

Yes, "it's the tone (or two tones; look up DTMF) that matters", I turned up the speaker volume and now it works.