By default PhoneTray uses your USB modem in exclusive mode and other programs cannot access the modem. If you need to share your USB modem with other programs, for example, Windows Fax or other fax software, you need to enable modem sharing on the Settings - Lines screen. To access the Settings - Lines screen, click Settings on the left navigation panel and then click the Lines button.
To enable modem sharing, on the Settings - Lines screen select Advanced tab for Line 1 or Line 2 and then check the "Enable TAPI mode" checkbox:
Please note that Caller ID detection could be less reliable in TAPI mode because PhoneTray has to use Unimodem driver for Caller ID in TAPI mode.