I have experienced WoW on the following:
56k modem - Playable, but you won't be able to do Battlegrounds or 40-player raids... the bandwidth requirements become rediculous and causes your latency to climb sky-high.
ISDN64 - Same as above, except you will be able to play Warsong Gulch BG, which is a 20 player BG.
ADSL shaped - If you're a serious online gamer, don't get this. For at least 6 days per month you'll be totally unable to play. Thank you Telkom... 6 days out of 30 equals 20% downtime per month, which is ridiculous!!!
ADSL unshaped - This is what I have (
www.saol.com), and is one of the best options available for people wishing to play games on international servers. Latency is always consistent, and the bandwidth is very acceptable as well.