Tracfone's home area and roaming areas depend greatly on where you register it as your "home area." It also depends which phone you have. From what I understand many of the newer GSM phones offer nationwide coverage, so charge 1 unit per minute all the time.
For non-GSM, check the coverage maps, and pick the one that works best for you. Tracfone contracts out to different carriers, which is why I am not roaming in VT, but someone from Vt might be roaming here (in RI). RI and MA are serviced by cingular - when DH calls me from his cigular phone it's considered in-network, and he isn't charged. I could have switched over ad added a phone on his plan, but I have over 1000 minutes built up on my phone from various promotions. (If you are referred by a current member, you both get 100 free minutes).
If you look at coverage for Burlington VT (05402), you see local coverage as most of VT, but that's it, and only phone with "national coverage" are available.
If you look at Portland ME (04123) the National Coverage phones have a small home area, and the Single Rates have spotty but broad coverage over the entire country.
Then look at Boston (02123) or Providence (02901) and you have good coverage for most of the eastern US. This is almost identical to the coverage map you would see for a Cingular GoPhone. If you use it less than 4 minutes per day (counting only the days you use it), the gophone will be 25c per minute. Or you can choose the other rateplan that's $1 per day of use plus 10c per minute. Tracfone will either be a bit more or less depending on how many minutes you'll be using over the course of the year. (you can activate it for each trip with a "local" number for that trip, and let any unused minutes expire after 60 days, or you could keep it activated to keep your minutes (In which case, I suggest an annual plan). If you have someone stateside who would be calling you, I would consider a number that is local for them so they aren't paying long distance charges.