To fix a "voice mailbox is full" problem, dial *86 on your mobile device; enter your pin number; press one to listen to your messages; press 7 to delete a message. You'll need to delete the messages one at a time. This problem occurs because Verizon only can store about 40 voicemails total, regardless of the length of the message. This storage bottleneck is occurring at Verizon, not on your phone, so just because you don't see any messages on your phone doesn't mean they aren't still lurking at Verizon. Yes, keeping on top of this is a pain.