That isn't vocoder, it's distortion... sorta makes it sound like a person talking on a phone, not a computer imitating a person.
There's vocoder happening BEHIND that, going on at the same time.
Here, I've gone into audacity so you can hear exactly where it is.
http://www.mediafire.com/?4d1r83qo5cd9jht
Part 1: "Danger" sounds like it COULD be distortion plus autotune, but it could be vocoder too.
Part 2: That "bwa-da, bwa-da" synth instrument in the background here isn't a synth instrument, it's a person "singing" nonsense through a vocoder.
Part 3: Not the rap, the main synth melody in the background. Sounds sorta like it could be words, but i have no clue what they are. By the nature of the vocoder's sound it's very hard to tell what the words are, but it doesn't just sound like a keyboard being played.
Part 4: Same thing as part three, but being played during a verse rather than the rap. Not the "ah-ha." As I mentioned, a vocoder is barely even discernible as a voice.
THAT is vocoder. It's used as an instrument through a good part of the song actually.
The voice saying "I'd like you to watch me until that day, that day" in "until that Day..." is also vocoder, and the voice saying "one two three four you and me" in the instrumental break part of "STEP you" is as well. In those cases no vocoder credit is given probably because it was a mixing/arrangement decision and a vocoder effect was placed onto something already recorded rather than someone actually singing through a vocoder, which seems to be what happened in Ladies Night.