They are still allowing signup
Vonage's webpage appears to be still allowing people to sign up.
Vonage is not allowed to sign up new customers while it appeals a court ruling that it infringed three Verizon patents. This is the price the VoiP telephony provider must pay for gaining some breathing space in its appeal against an injunction from using technology "owned" by Verizon. Vonage asked the trial judge to reconsider …
The problem is that "open-standard, off-the-shelf technology" doesn't protect you from being sued for patent infringement. Whether you developed the "open-standard, off-the-shelf technology", or simply use it, doesn't matter, either. We've seen more than enough lawsuits where the end-users of a product are sued for patent infringement, as opposed to going after the real infringers.
But if you think that using "open-standard, off-the-shelf technology" is any protection, just ask the various RAM companies who were sued by RAMBUS. Even an open standard can be blocked / blackmailed / sunk by patents.