Another well-financed VoIP company -- SunRocket -- is on the ropes.

Calls to the company's Vienna, Va., office Tuesday weren't answered. The company's 800 number elicited a terse response: "We are no longer taking customer service or sales calls. Goodbye."

SunRocket received more than $40 million in venture capital, and had a high-powered CEO, Lisa Hook. It had more than 200,000 customers a year ago. But it has been laying off employees in recent weeks and subscribers lost service temporarily a few days ago.

SunRocket is the second pure VoIP firm in the United States to experience difficulties in recent months following Vonage Holdings' well-publicized loss of patent litigation with Verizon Communications. Vonage claims more than 2 million subscribers.

Skype, which is owned by eBay, hasn't turned the profit corner, but the company has millions of subscribers.