Hi Sqly,
Have you ever used the voicemail before or is it the first time you are trying to use it / set it up? First things first, If you encounter ANY problems with your service or features like voicemail, you probably wont be able to fix it yourself and its a good idea to call into customer service and they may need to "troubleshoot" your line and correct the problem. They have access to certain tools and resources that the normal customer does not, and they use these tools and resources to fix problems with your account such as Voicemail. Best of Luck!