Despite an injunction against them, Vonage will still be able to sing up new customers while they are battling with Verizon. A federal appeals court has temporarily lifted the injunction, which formerly prohibited them from signing up new customers until they had settled the issues. This doesn't prove anything regarding whether or not Vonage is guilty of patent infringement, but should at least allow them to continue business as usual.
It's unlikely that Vonage will shut down, but they may end up paying gigantic fees if Verizon gets their way. Vonage asked for the injunction to be lifted mere hours after it was first placed.