To speak to someone about hotel reservations, call +41 21 962-8473. You can also reserve by fax using this form.
There are plenty of other good hotels in Montreux, and you are obviously free to make your reservations using other booking sites. But, if you reserve through the tourist office, you help UIST earn credit towards free rooms for the student volunteers. Please consider helping the conference in this way.
For something very inexpensive, you may also want to consider the youth hostel, which is a 15-20 minute walk from the casino along the lakeshore footpath.