you can change your number to another phone right off of the verizon page. you need to set up your online account first if you haven't already. they can also do it at the store for i think $20 or $40. they can transfer all of the numbers from the old phone and put them on the new phone as long as they both turn on and such. i think that is $10 or $20. as for cheap phones, don't know where to look?
