Well, we all know crippled and fake modems are just a big conspiracy to lock people into Windows. Here's what Microsoft has to say about them:

Keep soft modems out of retail. The installation problems of controllerless modems in retail are well known. Most end users don't have the computer skills needed to solve the problems that arise, generating support calls that exceed the cost of the extra hardware. Computer store salespeople report that they don't like to sell soft modems because they have a high return rate.
In a nutshell, the primary reason these things exist is because they let the manufacturers shave a few dollars off the cost of production, and the typical consumer prefers lower cost over performance and reliability. There's also the prevalent myth that "dialup is dead" and "everyone" is switching over to broadband. In reality, broadband adoption is stagnating, and 40-60% of all users still want the ability to use conventional telephone lines.

The traditional advice to "just use an external modem" is threatened: first, there are "fake" external USB modems on the market. Second, there's a push for even-more-cost-reduced "legacy free" PCs--that's a euphemism for getting rid of serial ports, parallel ports, floppy disk drives, etc.

That said, it is still possible to obtain "real" internal modems. Probably the easiest to find (in the U.S. and Canada; I can't speak for the rest of the world) is the USR V.92 Performance Pro. You can order it direct from their web site, or find it at places like Office Depot or CompUSA. CompUSA also stocks an IBM-branded controller-based product. The highest-quality products on the market are probably the Multi-Tech MultiModem ZPX line. For other possibilities, I'd look at shopper.cnet.com, click on Modems, then Internal modems, then Sort by Lowest Price, and work my way up, skipping anything described as a "winmodem," "softmodem," or "controllerless modem." If it says it works with Linux--or, even better, DOS or "all operating systems"--you have a winner.

If you're going to use an internal modem in a desktop machine, it really ought to be a genuine, controller-based product regardless of what operating system(s) you choose. The only reason to even bother with controllerless/softmodem support is for laptop/notebook computers, where having to carry around yet another device creates at least as many problems as it solves.