Phone System,5.8GHz,Expandable,2 Handsets,Caller ID,2-Way Expandable broadband system phone lets you take your phone conversations digital and across the Internet. Bundled with two cordless expansion headsets, it features handset speakerphone, two-way paging and built-in data ports. Broadband telephone system 5.8 GHZ technology is expandable up to four handsets. Works with model IP811 Dual handset system with caller ID/Call Waiting, one-touch access to Vonage Voice Mail. Includes set-up hands-free speakerphone in both handsets Vmode transfer calls and conference. Use an outside call or use the Intercom feature between handsets. Offers 50 name and number phonebook directory, call transfer and voice mail waiting indicator. Vonage certified VOIP system headset compatible. The VT8100-2 will only work with Vonage service.