Can Wengophone talk to "outside" SIP networks?

I’ve tried calling to and from my Twinkle Phone and Wengophone 2 with no luck. The Twinkle phone is set up running an Ekiga.net account, and it works calling to and from all sorts of SIP networks. Actually, every SIP network I’ve tried works other than Wengophone. Has anyone had any success here? If so, what am I missing?