How to read the technical specs for the iPhone 3G correctly
4 channels of AM radio


  Quad-band GSM/GPRS/EDGE
  (850 900 1,800 1,900 MHz)


3 channels of FM radio


  Tri-band UMTS/HSDPA 3.6
  (850 1,900 2,100 MHz)


Except that GSM+ and UMTS+ are a little more complicated than the old radio standards, but what you really need to explain to customers is what carrier they select means that not all of these channels and flavors of radio encodings will be active at any one time.

The capital letters are at the most basic, just different speeds of transfer on the same frequency channel so you might just gloss that over until the carrier coverage is compared to make sure that high or medium speed data will be provided.