A word of caution. No matter which carrier you go with. Put some thought into which manufacturer, model or phone you get free/small charge/or pay big bucks for. My wife has always had Nokia phone. The cheap free one. And we have no complaints about this phone. I have an other brand (older model) and Do not get the same reception and more frequent dropped signals. I'm sure its the phone we both have the same service provider. So ask about phone's and model #'s.
Also be sure the Phone you get is Tri Mode. Some phones are digital only and you won't receive the same coverage as one that will drop back to analog mode when digital service is not available.
The way it works is if company ABC doesn't have digital coverage in a particular area they may contract with another provider for analog service. This all takes place without U or I knowing about it.
With a National plan you will never know or most likely never see it on you bill, dependent on the company you choose. With Regional plan you may see extra charges for areas outside your coverage area and additional charges for roaming and maybe additional charges for analog service.
If you have a digital only dual band phone you can not access the analog signals because the phone is not capable. In fringe area's analog may be your only signal available. If you are full timing go with the national plan without a doubt.
AMPS is the Analog mode. It stands for Advanced Mobile Phone Service If you do a search on the web site below.
Good luck in your search
If you want you can go here to start looking for phones
http://www.phonescoop.com/