Unless the phone is analog/GSM or analog/CDMA, it won't have any analog capability as backup. On the other hand, analog is being phased out sometime before 2010. Right now, the FCC requires
Pick your phone (or at least narrow the models) BEFORE going to the store. Go to the Nokia, Motorola, LG and Samsung websites and pick out what features are important to you. Then determine what models have those features. The websites tell you what carrier has those phones. Then, go to the carrier store. If they don't have the handset you want, ASK. If the Nokia site says Cingular carries the 6xxx handset you want, and the store guys act ignorant, call the 800#. They frequently have more phones in stock at the central depots than the stores.
I invested in a high-end Smartphone (Symbian OS, camera, GSM, Bluetooth, EDGE) because I plan to use the same carrier for three years and the same phone. I've been very happy with it - but I've never seen it in a store and none of the clerks know what Symbian is.
But, I can use it with a headset or my car kit, it has every contact I might ever need in it, stores a bunch of pictures, downloaded games (Solitare) and, best of all, I can use as a digital modem for the PC at about 56k (using EDGE GPRS data service) without a cable, as the PC is Bluetooth.
On the other hand, at the time (a year ago) it cost me $199 where I could get a simple handset for free.
In the US markets, the handset makers are slaves to the carriers, since they subsidize the handset to the tune of $100-200 each, and require a 1-2 year contract. In the UK and Europe, people go to Nokia stores, buy handsets and then get service from someone.
Yes, the phone is, for all intents and purposes DEAD. When you get no bars of signal, you can't make a call. Cellular is NOT a 'cover the US' technology. Neither are SkyTel 2-way. If you must have coverage EVERYWHERE, get a satellite phone
Some of those areas will be out of luck as analog is removed. But, just because carriers won't activate a new analog-only phone doesn't mean it can't be used.
One of the little secrets that the cellular carriers DON'T tell you is that an unactivated phone can ALWAYS dial 911. If you're looking for pure emergency service, get one and leave it in your car trunk (with the cigarette lighter adapter, as the battery will be run down). Get it out and plug it in when you need help. The same goes for a old digital handset, except for range (remember the car cord)! The carriers don't tell you this, as some percentage of their paid market is for emergency use only, and if they publicized that, it would go away.
As John points out, most of this is due to the 850 vs. 1900 mhz difference. All non-bag/non-car handsets have the same 600mw output. No one ever (to my knowledge) built a 3w transmitter to hold against your head.
Why are they phasing out analog?
Spectrum usage: they can support more users on a tower, or on a group of frequencies using GSM or CDMA than they can with AMPS. Remember that the frequency auction for the 1900mhz PCS space raised $Billions for the US Government (selling what is already public). That's another reason the FCC is pushing for digital TV. They are going to reclaim some of the UHF spectrum, once the conversion is mandatory and complete, and auction it off for big $$.
Fraud: it's much easier to clone an AMPS phone than a GSM or CDMA one. It's also harder for them to figure out it's been cloned. The only thing that's saving their bacon is that fewer and fewer calls are analog, so any fraud stands out more in the pattern.