That extra twangy bit means the modems negotiated a V.92[1] connection instead of a v.90 connection. Just a newer protocol, that was a bit faster, but required cleaner phone lines to negotiate successfully.

I spent 6.5 years of my life working technical support for a dial-up ISP. Listening to the handshake (when the user had two phone lines so they could attempt a connection with us on the line to listen) was a valuable diagnostic tool.

[1] http://en.wikipedia.org/wiki/V.92