do you get phone service from you ISP as well? if so, then you need to keep your current modem/router combo (and you should go into its settings and disable its wireless). if not, then you can buy your own modem (i'm assuming you have cable internet and would thusly recommend the Arris SB-6141) and return the one you're leasing (and paying a monthly fee for) to the ISP. but either way, you can use the new router.