If the destination number is in the t-mobile network then they can't chose that the call doesn't go into t-mobiles network. They can control one part of it, th

If the destination number is in the t-mobile network then they can't chose that the call doesn't go into t-mobiles network. They can control one part of it, the point where their VoIP is transcoded and switched into the network, here could lie the issue. But the issue could also come from the destination end of the network. I generally believe that US and EU carriers are solid enough that calling there shouldn't cause issues, but who knows whom the parent is calling. Could be Afghanistan for all I know and I am not as confident here that there wont be any issues that are definitely out of control for Skype. In some cases the carrier might even wilfully degrade the quality because they want to earn more. They earn less if Skype routes a caller from the US to Afghanistan via IP and lets him call from a Afghan to Afghan number.