Narrow/Wide Band...it's all relative
Last Updated: 08/07/2013
There are two parts to this... frequencies and modulation.
The new commercial frequencies and those assigned to Mars/Caps operations are on 2.5 kHz steps. i.e., 147.2125, 154.6735 While the commercial radios can do these frequencies, many, if not most, amateur radios cannot.
Basically, amateur radios can do these frequencies to the fourth decimal
That's it!! You cannot dial others in from the face of the radio even with the step set to 12.5kHz. The internal components of the radio just cannot generate other frequencies to the fourth decimal. So, while in the example the radio would be able to do 147.2125, it would not be able to do 154.6735 (the closest it could get would be 154.6625 and while it might hear the signal, it could never transmit well enough to be used on that channel.)
Newer radios can do 6.25 Khz steps giving them the ability to tune more frequencies. There will still be those that they cannot acess (i.e., 154.6735 in this example - the closest is 154.66875 then the radio steps to 154.675.)
These newer radios can do:
While this gets you more frequencies and even tuning to the 5th decimal point, lots are missing... and you cannot tune to them.
Radios that do 2.5 kHz or .5 Khz frequency steps can tune to the "new" - frequencies. As of today 01/16/2012 the Kenwood TH-F6 and TH-K20 and the Wouxun KG-UV6D are known to have these step sizes available... not to say there are not others.
When you transmit the signal modulates above and below the frequency by 2.5 (narrow) or 5 (wide) hertz. This is just how radio waves work. On most radio, narrow modulation is set up for a memory channel with though a check box for "Narrow" or as FMN (FM Narrow) as the operating mode.
If the radio has this option, it will be in the programmer in one of these two ways.
The most important part of listening is being able to tune the frequency. As far as listening on Wide or Narrow FM
Ultimately, if your radio can tune to the frequency, you will be able to hear it.