CB Radio or Cell Phone
Yes, a 2 meter ham rig is a nice thing to have when travelling. However, reception and distance of transmission IS quite limited, as is what you can legally use it for. As entertainment, or between members of a caravan, it can be tops, but you still will want a cell phone to talk with the 'real' world.
Generally, with the ham antenna and power appropriate for a standard vehicle, 20 miles is about the best you can hope for with 2M and/or 70 cm, under ideal conditions. If you are within range of a repeater, than you might be able to extend your range to 40+ miles. Some, but not all, repeaters have the ability to make phone calls, and in many cases, this ability is limited to a particular group of people. Also, since the telephone call is being transmitted over the ham band, all ham regulations apply. Since business use is prohibited, it is possible that calling for a motel reservation could result in massive fines. Receiving a call via ham radio is impractical under most conditions.
There are other ham bands available which have substantually further range, but they may not be used without a more involved test than that mentioned above, are 'unreliable' due to a high dependance on weather conditions and do not (as far as I know) have the phone call capability. Besides, these bands generally are most effective when using a directional antenna, which is not practical while driving.