In order to achieve a V.92 connection:
The server you're dialing in to must support and provide a digital V.92 signal. Your ISP can provide you with a list of dial-up connections and information on what those connections currently support.
The telephone line between your ISP and your modem must be capable of supporting a 56K connection and contain only one analog-to-digital conversion.
Your modem must be connecting to a V.92 server. A pair of 56K modems will connect to each other at V.34 speeds (33.6K).