Yes. Please take a look at the following URL:
There's a section on SIP Clients, including both Free/OpenSource as well as commercial software. X-Lite and SIP Communicator, among others, run on Linux.
I've been able to connect to the server successfully and REGISTER with X-Lite 2.0 for Linux; haven't tried placing a call, though. No speaker or mic connected to my Linux box. Give it a try.
Instructions on how to configure X-Lite v2.0 can be found at: