said by DMS1 :

I would have thought that this is more likely to be Packet 8's problem than Vonage's. VOIP companies don't own any phone numbers. Instead, they partner with CLECs that provide the numbers, since it is them who are responsible for terminating incoming POTS calls. It sounds suspiciously like Vonage and Packet 8 were using the same CLEC in this case and somehow when Packet 8 assigned the number originally it didn't get removed from the CLEC's free-number pool. In this case, Vonage would have assigned it in good faith.