Botox can help flatten the sagging neck vertical bands. The treatment never gives the same good result as a surgical neck lift. The horizontal creases may or may not respond to Botox treatment.
Patients are evaluated in person by a board-certified physician to determine how many units they would need. Every patient is different, and in fact, the same patient may need more or less on successive treatments and are reevaluated each time.
The information provided in Dr. Shelton's answer is for educational purposes only and is not intended to constitute medical advice. The information provided should not be relied upon as a substitute for consultations with a qualified health professional who may be familiar with your individual medical needs.
Web reference: http://www.thenyac.com/botox/index.html