From what I've read on the cell phone forums the big providers will all drop analog shortly after the allowed date but the small guys may still keep it around. I've noticed that most of the time now when I am getting an analog only signal its extended network or roaming which means I'm on one of the small providers towers so you may still be able to get an analog signal.
However, I've limited myself in the past to tri mode phones and last time there were not many to choose from so I ended up with an LG which turned out to be the Kia of phones. Since Verizon is now allowing their new every two credit 4 months early (20 months for the two year contract) I'm going to get a decent phone and am not going to bother with analog. My thoughts are that even though some of the smaller companies might keep it around there is no gaurentee for how long and I probably won't get any notice when they turn analog off so I may never know until one day when we try to make a call. I'm supplementing my cell phone with other methods of communication such as CB and ham radios.