Unfortunately I have to admit that his closed-source software is the only softphone for Linux that works with every SIP provider I know. It also has a decent call management but sometimes drops calls while it should be holding them.

The GUI of this software is nothing but a big pile of crap. Proportional fonts clipped uglily on the borders of a fixed-size bitmap window layout combined with an extremely unintuitive menu structure and -handling and totally custom-made input widgets which dont behave as you would expect.

But after all and once you got the hang of this usability-nightmare, it just does its work better than all the others. Sad but true.

Normally I would rate this software not better than "good" because of the badly flawed UI, but given the fact that there are very few considerable alternatives rating is raised to "very good".