You can do this from the automated prompts when you call 888-294-6804: (no need to talk to a person)
Then choose LOW from the available choices, this disables the pre-call notifications.
These prompts are no longer correct.
If you want those annoying balance messages at the beginning of every call to go away, what you have to do when you call 888-294-6804 is choose 7 for 'other options,' then either say "change balance notification level" or else wait for the numbered choices and pick 2, 3 and then 1. Now choose LOW and confirm your choice. And then you won't hear that annoying message at the beginning of every outgoing call anymore.
Hope this helps!