A VoIP adapter for POTS a phone comprises: a POTS phone connector, an IP network interface, two sets of signaling senders, signaling receivers, media senders and media receivers for the POTS phone and the IP network respectively, and a controller for controlling the operations of above components. The VoIP adapter enables the user to carry out VoIP communications using a normal POTS phone and further enables use of advanced VoIP functions via the normal POTS phone, such as Call Hold, Call Transfer, Ad Hoc Conference, etc.