Introduction
Equipment that attaches to the public telephone network, called section 68 equipment, is assigned a different number by the FCC than most other computer equipment

By using Driverzone.com’s online database and the FCC registration number, you can quickly look up the original manufacturer of the equipment.

The difference between the FCC Registration number and the FCC ID
There are two different FCC numbers used for identifying computer equipment, the FCC Registration number and the FCC ID number. The FCC Registration number is used for "Connection of Terminal Equipment to the Telephone Network" or section 68 equipment. For a guide on how the FCC ID can be used, reference this guide. http://www.driverzone.com/guides/find/fcc/fcc_p1.html

Finding the FCC Registration Number
In most cases if the equipment is in a case it is on a small sticker, in the back of course.
Or if it is an add-in card it is usually etched directly onto the PCB as is the case with this modem:

Searching using the FCC Registration Number
The first three or four digits of the FCC registration number will uniquely identify who the manufacturer is. I find that using only the first three digits returns a better. So in the previous picture with a FCC Registration number of 4X2USA-25314-M5-E, 4X2 is what we want to search on.

So if we head on over to http://www.driverzone.com/fcc_reg.htm and enter 4X2 into the search box, we find that, that modem was made by 3com. Actually multiple records are returned for this search, but they are all different divisions of 3com.