I would recommend using this AT&Tvoip phones~
The Syn248 Deskphone is the AT&T VoIP phone that when used in conjunction with a Syn248 analog gateway will create a professional small business phone system for up to 24 phone users using up to 8 PSTN trunk lines (using 2 Syn248 gateways). The Syn248 deskset features a 2.75in LCD display, 9 programmable feature keys, a hands free speakerphone, built in voicemail and message waiting indicator (MWI).