And I thought that unlimited AOL for $20 was expensive... your plan is expensive as heck. Isn't there high speed internet such as Cable, DSL, or a WISP (Wireless ISP) around for you? I've had DSL for 4 years now, upgrading my speed twice and man is it a lot better than dial-up.
Otherwise, dial-up unless you have dual lines or ISDN or something, at a full 48000bps connection rate with compression, you'll see roughly 36kbps or 5KB/s download, and 67kbps (~7Kbps) upload including all overhead associated in dial-up connections for both download and upload. Is the speed test site you're using correct or is it just giving false data? What's the connection speed that your operating system is saying the modem is connected at while it is connected?
Also, don't confuse KiloBYTES with KiloBITS. There are 8 bits in a byte, so 8 bits per second (bps) comes out to be 1 byte per second (1 Bps), and 8 kilobits per second (kbps) comes out to be 1 Kilobyte per second (Kbps).
Also as a note, if you are not getting the full 48000bps speed, this can be because of a few reasons. First of all, make sure you dial into a number as close as you can get to you, make sure both your ISP's server and your modem can handle 48000bps speeds (V.92 modems these days are cheap and can certainly handle the speed) and make sure that your telephone line is in good shape. Old, degraded, noisy/lossy or long copper loops from your telephone company or in your home can cause dial-up to not connect as fast. The same applies for DSL. The farther you are, the longer your line is, the older it is in many cases, wire gauge, etc will affect a DSL connection's reliability and speed. The distance factor and noise factor applies for wireless connections, and for Cable, basically the same thing as DSL but in a different scale and perspective. Basically, anything that can affect DSL will affect dial-up, and vice versa.
EDIT: Also, considering I think your actual connection speed is 28000bps, I'd ask in the computer forum for some help with the connection as something's probably going on with it.
Also as another note lol. When doing a file transfer, transfers are measured in Kilobytes/Megabytes/Bytes/gigabytes/etc and connection speeds are measured in Bits/Kilobits/Gigabits/Terabits/etc.