According to the license agreement you can use one license of PhoneTray on two computers in your household. If you want to use PhoneTray on more than two computers you will need to buy additional license(s). If you want to use PhoneTray at home and at work you will need two licenses as well. Please note that you will need an USB voice modem for each computer because PhoneTray will not work without a modem. Please refer to the list of recommended modems.