Short answer is yes, but I would stick with a plan, because this phone is not worth paying $45/$60 per month to use. It only does about 75% of what a real smart phone does.
It is the best choice for the $30 plan, but for the $45 plan choose a real smart phone to take advantage of what you're paying for. You won't be happy with the limitations of the 840.
FYI, I love the 840. It is by far, the best budget phone around. I am a light user, on tracfone. But if I were going to pay $45 a month, I'd choose a real smart phone.
Yes you may use either plan with LG 840G.