Your best bet here is to actually post the brand and model of modem you're looking at. (Pardon my dangling preposition.)
Also, if you are looking for a modem to buy, many suggest an external modem, such as the ZOOM 3049, which I have.
I have not read that the DSP (digital signal processor??) makes the modem a 'hardware' modem, but I could be wrong about that.
Here's another thread about modems that mentions DSP.
Don't V.92 features have to be supported by you ISP? Sorry, I'm not yet familiar with V.92 support in Linux, although my modem is a V.92 modem.