Hi,
I noticed something...
First I was reading through
DIDWW DID calls not received
DID World Wide Question
It seems DIDWW has a test page
DID World Wide, International DIDs forwarded to PSTN and VoIP by SIP, IAX, H323, Skype, Gtalk, MSN Messenger. Origination services, SIP DIDs
So I ran a test with my VoXalot acct., and what I noticed was that calls to my VoXalot acct. were only successful when I chose USA as my preferred server