Xten is good for "telephone" like functionality. It has DTMF support, has inbound/outbound proxy settings, has an onscreen keypad. It doesn't do Presence & Messaging. It also supports uri dialing where the address specified is alpha-numeric instead of the usual numeric only telephone number.
Wave3software makes Session. It has inbound/outbound proxy settings, does not yet have an onscreen keypad but this is coming. The latest release does Presence & Messaging. It supports alpha-numeric uri dialing. It also supports video but with a very restricted set of cameras.
You can check out Microsoft Portrait. It is a free soft client that looks and feels alot like W> Hi,