Junejuno - I've worked at a few placed that do botox. If you want to introduce this to your spa, I would highly recomend that your spa be a "med-spa" (with laser, microdermabrasion, peels, etc). I also recomend that you hire an MD or nurse to come in and perform the botox. Good luck!
Claire - I don't know what the laws where you live, but here in Canada, Medical Estheticians CAN do botox... Although very few will ever be hired to do so. Most med-spas will hire a doctor/nurse to come in once every week or two to perform injections.
I went to school with a girl though and she is doing botox now on clients, so don't give up if you really want to do it!