Make sure that your voice mailbox is not full. If it is full, then you will get a busy signal. If it is not, then dial *73, just to make sure. Then dial *228 and select Option 1. After this is complete, pull your battery and reboot your device. See if it works after that. If it is still not working, then call customer service from your device at *611 and they might have to reset your voice mailbox.