The old route was broken and installed a new one (verizon brand). Initially the spa1001 couldn't register to voipdiscount. With Mr. fitwxc's help I disabled firewall and it started to work, call in and call out (only tested for a few seconds).
Today when we call China it always got disconnected after about 10 seconds's talking.Searched and read many posts including Mr. fitwxc's "網絡電話的工作過程,問題所在和解決辦法", but still couldn't figure out the reason.