Them new-fangled contraptions

Rob and I are thinking about getting a cell phone. We want it mainly for emergency and urgent needs (e.g. if babysitters need to get a hold of us while we're out, if our parents should need us for a medical emergency, if I get a business call that needs an answer now). I know once we get that little convenience devise in our hands we will use it for other things, I just don't foresee a lot of use - thus we don't want to spend a ton of money.

We hope to start taking vacations, too, so availability while out on the road is rather important (Canada and US).

As we are new to the whole field, I'm wondering if anyone has some advice on what company you have liked, what to consider in a contract, what to look out for, what you think is the best deal - that kind of thing.