There are routines available that calc the distance between two addresses once the latitude and longitude is determined. However, that is not worth much unless you are flying.
We went through the same thing and finally ended up with MileMaker from Rand-McNally. It is the product used by many carriers to determine traveling distance between two addresses. This is frequently the number used by moving companies.
They have several versions of the software, one of which runs on the iSeries. Its pretty easy to use. It comes with a callable routine which returns the miles between two addresses. No need to know the lat and long.