The VIP-157S is a 2-port Analog Telephone Adapter that features 2 FXS connections, so you can connect 2 analog phones, an analog phone and a fax machine, which allow you to use your existing analog phones or fax machines to make calls via the internet. The VIP-157S supports T.38 fax and works with most SIP-based internet service providers (ISPs). The VIP-157S is a great choice for voice service providers because it is completely customized auto-provisioning, auto-update.