 External modems were available for these platforms but required the phone to be dialed using a conventional  making them unable to accept incoming calls without manual intervention.
<clarity>  External modems were available for these platforms but required the phone to be dialed using a conventional  making them unable to accept incoming calls without manual intervention.
 External modems were available for these platforms but required the phone to be dialed using a conventional handset, making them unable to accept incoming calls without manual intervention.