If you’re prompted to enter your PIN (four digits), it means that Skype To Go™ does not recognize the phone number you are calling from. Make sure you've registered the correct phone number or are calling from a phone number you previously registered:
If the number is correct and you’re still being asked for your PIN, then it may be due to your caller ID settings. If your phone is set that it does not display the caller ID, this will prevent Skype To Go from recognizing your phone, and you’ll be asked for your PIN before you can proceed with the call.
To ensure your phone can be recognized by Skype To Go, make sure you have caller ID turned on. You can test this by calling a mobile phone to see if your phone number shows up. If not, you can call your phone provider for support, or find instructions on how to do this on the phone manufacturer’s website or in your phone’s manual.