Perfect for small businesses that need two-line support. Fully integrated answering machine makes it easy to screen calls and check your message while away. Large, easy-to-read display clearly shows phonebook entries and Caller ID information. Compatible with most headsets via 2.5mm jack and hearing aids. Answering System: Digital Lines: 2 Telephone Type: Corded.ATTML17939. ML17939. At&t At&t ML17939 Two-Line Speakerphone with Caller ID and Digital Answering System.