This is not completely correct.
Yes - you should at all times join both a tradeskill society along with a wholeseller society, as long as SoE hasn't chosen to change it.
Apart from that - you should check out this website - it explains it all to you along with a lot more:
website You will soon find out that you should join a wholesale society first, lvl up your tradeskill to lvl 10. Get a certificate for the trade-area you would like and then join the tradeskill society that fits your new certificate.
In each city-area should you be able to find one of each time of tradeskill society, so it does really not matter where in the city you chose to live or work. It all depends on you.
Good luck in the future.
Edited, Sun May 29 12:56:52 2005 by Antara