If you're going to try it with Directway, it definitely wont work. The turnaround times on the satellite are WAY too big for voice. What you'll get is broken gargling voices with 1-3 second delays between when you start talking and the other person hears the funny noise.
Oh yeah, i forgot. One of the biggest problems with the old sunrocket gizmo is that it frequently decides to allocate half of your ISP bandwidth to implement "quality of service", which is swell when you're on the phone and not using the computer, but not so good when you're on the computer and not using the phone.
Disconnect your gizmo and see how fast your connection is by using a speed test like those at DSLREPORTS. Then put it back and see what the speed looks like.
Another good site for looking at whether voip will work on your ISP and for troubleshooting problems is www.testyourvoip.com
Sunrocket tries to get you to use a site called "internet frog", which is so overloaded that the server cant service all of the requests and therefore it gives erroneous results that your ISP is too slow to respond. That works out well for sunrocket, as every customer problem always turns out to be a "bad ISP".
Good luck trying to explain this to the customer service rep and getting them to look at the results from other test sites that show that your ISP is fine.