True, I also had a E60 with integrated SIP. I had a very bad experience with that. It was unstable and didn't work that well for me. So I mostly used the client on the N800. Also the N900 integrates other VoIP services like skype. But it is true that S60 may have been earlier (don't know if Maemo on N800 or S60 was first). Later nokia removed the SIP integration in the S60 phones, don't know if they enabled it again in phones like n8