Having used IP Telephony for a number of years I need a workable SIP client for all of the devices I use. I have found a very capable client for my Android phones (SipDroid) and on Windows/MacOSX I generally use X-Lite (as well as it’s paid version EyePhone) from Counterpath.

Having tried several different Linux SIP clients (Ekiga, Twinkle, …) but all discarded them because of weird UI’s and/or problems with stability I noticed that there is a Linux version of XLite available. Unfortunately on current versions of Ubuntu (10.04) it needs a deprecated version of a library.