You mention an 802.11 card-- which one?
There are two different technologies used in the old 802.11 (non-b) cards: Frequency Hopping, and Direct Sequence Spread Spectrum.
Most 2.4Ghz phones use Frequency Hopping to try to cope with noise in the band. The problem is that other frequency hopping devices in the same band may get very near into phase with each other, causing noise most of the time! I suspect that your 802.11 card is a freqency hopper.
The later 802.11 cards (and all 802.11b equipment, like the Lucent gear in this article) use DSSS, which uses one of eleven possible 'channels' and does tricky math to work around errors. This stuff tends to do better in the presence of FHSS, but worse in the presence of other DSSS equipment on the same (or an overlapping) channel.
Incidentally, I didn't throw a 2.4G phone into the test environment for this article because I don't own one (donations gratefully accepted! =) Although I do have friends who use them happily right along side their home 802.11b networks.