Our system can work with handsets that support SIP over the UDP or TCP protocols.
We do however use and recommend the Yealink range of handsets including the T48S, T46S, and the W56P for those who require cordless handsets. We find that these handsets are quite reliable especially when used in environments that can otherwise cause problems with SIP such as where NAT (Network Address Translation) is involved.
Concordant can provide and optionally pre-configure Yealink handsets for use with your services. For more information, please contact your account manager.