I started out my first year in Ithaca with AT&T Wireless. That was an absolutely horrendous experience and I couldn't wait to get rid of their utterly terrible service. I checked around and the majority of people that I knew either had or had switched to Verizon for as their wireless carrier.
I decided to follow suit and it has been great. I actually get service in Ithaca now. It is better in some areas, but coverage throughout is pretty good.
If you are coming up and are looking, this is definitely your best bet. Only other alternative to consider is Cingular. Sprint also has a store there and tries to lure you in saying that they are building a tower in Ithaca and just waiting for clearance. I heard that story my second year and have heard that Sprint is still spewing that garbage. Unless there is a fully functional working tower, don't listen to what they say.
Verizon might be a bit on the expensive side, but since most people, especially at Cornell, have it, you end up using a lot of "IN" minutes which are free anyway so you can actually downgrade to a cheaper plan.