Sunrocket is a VOIP provider, which means their main product is a telephone connection running over an IP network, which is in most cases, the internet.

Sunrocket has closed it's doors.

SunRocket will cease operations at COB today. As such, today is my last day and everyone else you may have worked with at SunRocket.(GigaOM)

What happened ? Not too difficult to imagine. With all the competition in voip providers, the company went belly up as a lot of people now have found their ways to (almost) free VOIP available on internet, or the good offers quality IP's now offer including VOIP lines. Competition.

Webware goes into detail on this subject.