Was able to get visual voicemail to work today by doing the following:
From XDA
1. Go to your VVM
2. Press Menu and choose "Compose"
3. For recipient To:__________ type in "activate@vvm.sprint.com" (no quotes)
4. Press Record then Stop
5. Send (you may have to make a display name.
6. Reboot
I still can't get the activation message to send... I remember I tried this a while ago as well, as ran into the same problem (error t-30). Any suggestions?