"We have seen an instance of port blocking that was of grave concern to us," Vonage spokeswoman Brooke Schulz told Reuters. "We have sought the FCC's council to remedy the situation."
Voice over Internet Protocol, also known as VoIP or IP telephony, is basically the transport of telephone calls over an internet connection. Until recently, it was a niche phenomenon, but VoIP now has hit the mainstream consumer and business markets, offering cheaper calls and disrupting the dominance of the traditional communications companies.
While VoIP software allows a broadband internet connection to double as a telephone service, ISPs can, if they wish, control the use of that connection by blocking certain network ports. This technique is often used to try to combat unsolicited commercial e-mail, but it can also be used to block the digital data that makes up an on-line telephone conversation.
According to reports, Vonage began an investigation after consumers complained that they could no longer make VoIP calls. The company found that certain ports had been blocked, but managed to reroute its customers' calls temporarily.
Vonage has spoken informally to the Federal Communications Commission, but has not filed a formal complaint.
"We're very actively on this case and we are taking it pretty seriously," FCC chairman Michael Powell told tech news site Advanced IP Pipeline.