For FPS games (or any game where reaction time is crucial) Sub 200ms pings are near critical, sub 100ms preferable. most BF2 players running ADSL come in at around 40-50ms.
ISDN128 is usable for BF2, which is a bandwidth hog. I currently use ADSL192 and its also fine, for a single player, and don't do anything in the background.
As everyone else said - Wireless currently isn't good enough for "twitch" games. Having said that, apparently HSPDA advertises itself as low latency, so if you can get a demo from a vendor try it out before you take our word for it.