problems with skype and voipbuster

Hi

I have much delay on the incoming sound and almost no delay on outgoing when
using Voipbuster, but if I try Skype the incoming delay is low but the
outgoing is not coming through at all..
I have my own NAT router wich I have tried to opened a port for the voip,
but still it will not work.
Why the difrent problems with Voipbuster and Skype? Can anyone maybe give me
an advice on what to do or try?

Thanks,
Jakob

jakob