Verizon wireless contract help PLEASE!?!?

okay so i have a verizon wireless contract. im eligable for an upgrade in october but my fone is a piece of crap so i want to purchase the thunderbolt, i have to pay full retail price to get it now unless i wait till my contract is over. i cant afford retail price but my phone sucks and i really want this one. my account has two lines. mine and my grandmothers. if i cancle my line, how much would the cancilation fee be for the samsung alias 2? and if i went ahead and cancled it and only kept my grandmothers phone line, would i be able to open up a new line and just pay the three hundred something for the new two year contract? what should i do? would cancling one line then opening up a new one be cheaper than just paying ful retail price, which is 556$ (or whatever the price for it is) or for the new two year contract it would be 309$ (or whatever the price for it is.) not to mention if i replace this one or cancle and open a new line id need to buy a car charger cuz i travle alot, a universal charger, and a 20$ phone cover so i dont scratch it. so all in all, how much is a cancilation fee when im eligable to update in four months?, and would i be able to open up a new line and it all be cheaper then just paying full retail price? PLEASE HELP!!!!