Perhaps more interesting than the client itself is their claim that they’re the first to bring SIP support to S60 devices. From this page:
“Download the first Symbian mobile SIP client in world” [sic]
Unless they mean the first Symbian mobile SIP client purposed for O-FONE, I think they might be forgetting about Fring. Fring, which supports SIP (along with Skype, Google Talk, Twitter, AIM, and Yahoo), has had a Symbian client since March of 2007.