Pros
As CallWave recently laid off most of its employees and appears to be in the process of trying to sell its remaining assets, there aren't very many reasons to work there. When CallWave was in its prime, it was a model example of a traditional software development firm, with mature processes, detailed documentation, and a complex infrastructure. Now, development has been outsourced.
Kontras
CallWave is surviving off of an obsolete product with a shrinking market, and has failed to transform the underlying technology into something relevant. As the company recently laid off nearly all of its remaining employees, I would wait until they come up with a viable strategy before going to work there.