Softphone online status

hi all,

Probably reaalllllyyy simple this one, but is there a softphone, sip or iax, that can show what other extensions are registered. For example, lets say i have a simple office setup with 5 extensions 5000>5004 where some are soft phones(road warriors), and the other are standard hard phones, say a grandstream for example, is it possible to either:

a> have an indication on the softphones which extensions are on and registered, or b> is there a small application that can connect to asterisk that will show the status of each extension. IE registered or not.

I suppose it is akin to a buddy list within skype, showing which buddies are online and connected.

Any thoughts.>??