You obtained one of these from either Highhold Pass or Felwithe. I believe those are the only two cities. These were to be for "promised" housing at release.
From IGN: EQVault back in 1999 Quote:
2) "Houses". Feedback from 989 has been inconsistent. There are places where you can buy a house key, but it goes to nothing and does nothing. It has "Rent" of 0 copper a month, currently, and indications from 989 indicate that these will go to the (currently empty) rooms scattered around the cities, and will be both very expensive and limited in number to those that are already in the game.