Internet calls with liquid Z110

JWGRU

I recently bought the liquid Z110 and I aim quite satisfied with the smartphone. I found that its android OS in principle allows to make internet calls with the phone. I do that already with the application of my sip provider voipbusterpro, which runs very well on this phone. However, I would find it more comfortable if I could from the dialer directly call via the internet call option whenever WIFI is available, while otherwise I would call via the SIM card. Outside my home country I switch off my SIM card, since phone calls with roaming are still too expensive. With voip its just 2ct€ per call within the EU. When I choose the Internet Call option it says that it sets up the phone connection but then it close with the remark no response. I don't get any error message.