Were you ever able to resolve this issue? If so please come back to this thread to provide an update so others can benefit from the solution. I would make sure to ask Hoiio to perform a call trace/debug from their side to see if the NetVanta is sending something they are not expecting. If the SIP provider is unable to help resolve this you can post the debug and configuration to our FTP server with the instructions below and I would be happy to take a look.
Open Internet Explorer web browser
Type the following URL: ftp://ftp.adtran.com
Press the Alt key, click View, and then click Open FTP Site in Windows Explorer
Double-click the "Incoming" folder
Drag and drop files from PC into the Internet Explorer window
Reply to this post with the exact filenames used so we can retrieve the files