I see it's your first post here, so welcome to the community! I see from your account notes that you've previously been able to make calls, so when did this start happening?
Is there just one phone plugged into the ATA?
Please try power cycling your HughesNet Voice ATA by unplugging the power cord from it and replugging it after waiting 30 seconds. This would also be a good time to double check all your connections to ensure both ends of all the cables are secured and inserted into the correct ports. For your reference, you can view the proper setup in pictures in the manual.
Let me know if you're still hearing the busy signal after power cycling.
We're closing this thread since we never got a reply from you. If you still have concerns, please start a new thread and include a detailed explanation so we can more effectively help you.