I'm pretty sure you can figure out what that number's all about, but what if you wanted it for your own? How would you know whether it's taken.
Maybe there's another, easier way, but here's one way I found. The TN Database lets you cruise for potential phone numbers with a fairly simple interface. First you choose an area code, then an exchange, then you can narrow down the choices by the first two digits of the four-digit suffix (i.e. 800, then 423, then 56xx to get close to a number for my current employer).
The database won't tell you who holds a given number, but it will tell you, usually, if the number is assigned.
In the case of 1-800-328-7448, however, the assignment comes up "unkown." As does, oddly enough, the number for my current employer, and that of a former employer, too.