Can't use a pager in an Airplane as it is an RF device and should also be turned off. Company pay for the phone? Would they tolerate the time it takes you to hunt up a phone to call back? You might find that, for the coverage, a phone is about the same cost. If you don't use it heavily you might look at the various pre-paid plans. Buy as little or as much phone as you want and pay for the amount of time you expect to use it.
Another question - In this day and age, will your clients/customers/employer tolerate you having a pager, or do they expect/demand that you have a phone?