840G will work if the other phone will work.
There is no difference.
If the LG800G worked in your area so will the LG840G
runninron69, check the actual Tracfone website, to determine whether the LG840G will work in your area. The WM site isn't accurate, as to coverage areas. That being said, since this phone operates on the AT&T network, if you (or any of your friends) have used AT&T in your area, this phone will work, also. I hope this helps.