The round is expected to be Vonage’s final before it either goes public or is bought. Total funding in the company now stands at $658m.

This latest round of funding validates Vonage’s leadership in the broadband telephony market, said Vonage chief executive Jeffrey Citron, in a statement.

The company declined to comment on rumors that an initial public offering was in the works. However, the industry was buzzing yesterday with speculation that Vonage was pursuing an IPO as its preferred exit strategy. A second-choice option would be to seek a buyer, according to industry pundits.

Vonage plans to spend its latest round of money on building out its US network, including the deployment of enhanced emergency 911 capabilities. It may also expand its services abroad.

The latest round included 16 new investors, as well as existing backers, Citron said. This proves the financial community is confident Vonage is executing on our strategy to redefine the way people communicate, having already shifted the telecommunications landscape to an IP-based world, according to Citron.

The latest financing for Holmdel, New Jersey-based Vonage was issued in five-year convertible notes. They could be converted into stock if Vonage became public.

Bain Capital led the recent round, which also included New Enterprise Associates and Meritech Capital partners. Vonage senior management also participated.

Vonage holds the number one spot in the US VoIP market, with more than 1 million customers.