A couple of years ago, we discovered that AT&T geoblocks all VOIP traffic from India. We sent some configured phones to them, because the bosses were told by AT&T that it would work fine. Nope. All the tracert results clearly showed them dropping the traffic. But then a few months ago, it started working! The India team emailed me asking to change out the names/extensions, and since then we've had no problems.

Of interesting note: In Windows NT4 and Windows 2000, Interix / WSU were "add on" components for Windows. But starting with 2003 R2 and going through 2008 R2, it was built in. Then it was discontinued. Then revived with the totally different system that we have today.

Interix became integrated as a component of the regular Windows OS distribution as a component of Windows Server 2003 R2 in December, 2005 at release 5.2 and was a component of the Windows Vista release as release 6.0 (RTM November, 2006). Windows Server 2008 had release 6.0. Windows 7 and Windows Server 2008 R2 included SUA 6.1. - wikipedia