There are many ways to get your custom voice mail on your phone. Unfortunately most cell phone company's don't give us a way to transfer the file directly. For the technically advanced we recommend the free services of YouMail they make uploading files easy.
There is one sure fire way that will work with any voice mail system. It's a little low tech but until the phone company's catch up to us it actually works really well.
The first thing you need to do is set the volume level on your speakers. You can click on the play button on a beep any beep on the left. Adjust the the volume to a comfortable level. It should be about as loud as you would be talking.
Next you will need to get your cell phone ready. You'll want to get it to the place just before you press a button to record your voice message. If you don't already know how to do that you can listen to the prompts that play after your voice mail or check with the service provider.