What Does "Modem" Mean?

I'm still amazed that there's problems in communicating across radio systems. 25 years ago engineers had solved the problem of converting analog sound signals into digital signals and back in something call a "modem". (Anyone remember when a modem had a cradle for the phone receiver?) Surely you could kludge up a partial solution to the problem without much effort. But I guess FEMA and DHS never made a market for such solutions. Did they hope to convert everyone to the same system? That would be optimal, but the best is often the enemy of the good.