Hmm years ago there were these SMS to e-mail gateways. They'd e-mail you when SMS was arrived, some even with content. Heck, there were also solutions for the other way around. But this was before the .comboom.

As for killers. All you need is SIP and an application which handles the codecs for the audio input, audio output, video input, video output, and perhaps indeed text input, text output (for IM or SMS).