Certainly. 2.4GHz cordless phones come in various flavors.
1. 2.4 DSSS: Will coexist just fine with 802.11b/g.
2. 2.4 FHSS: Will clobber any 802.11b/g on any channel.
3. 2.4 FM: Will clobber 802.11b/g but only on some channels.
4. 5.6/2.4 cross band: No clue.
From your question, reading between the lines, it appears that you are
looking to buy a cordless phone that will interfere. Normally, a
microwave oven is sufficient to obliterate communications, but that
burns too much power. While I don't condone such practices, methinks
the FHSS (frequency hopping spread spectrum) 2.4Ghz cordless phones
will do the maximum damage. Most Panasonic phones are FHSS.
I can confirm from personal experience that 2.4 GHz cordless phones do
not play nicely with 802.11b/g networks. The problem was reduced, but
not eliminated by switching the channel on my WiFi.
Get a 900 MHz phone instead of 2.4 GHz -- it won't cause interference
and it will probably sound better too.
The only way you can be sure that there will not be a problem is to
buy a 900Mhz cordless phone. Just to add to the confusion, some
2.4Ghz cordless phones confuse DSS with DSSS. DSS means "digital
spread spectrum" which could mean FHSS (frequency hopping spead
spectrum) or the more desireable DSSS (direct sequence spread
spectrum). Anyway, watch out for the acronyms. If you're buying
2.4Ghz, it should be DSSS (Direct Sequence Spread Spectrum).
Also, watch out for cross band cordless phone. Panasonic Giga-Range
uses 2.4Ghz and 900MHz. The base transmits on 2.4GHz and receives on
900MHz. The 5.6Ghz version does the same crossband thing with 5.6Ghz
and 2.4GHz. I don't recall which band is used to transmit on the
base. Anyway, don't assume because it's a 900Mhz or 5.6GHz phone that
it does NOT use 2.4GHz.
I once found a table on the web comparing cordless phones which
included frequencies, modulation, power, and sensitivity. Of course,
I can't find it again. Sigh.