I'll start with a quick tip:
I own, and these are in use in my home, five cordless telephones, in addition to some fully-wired ones. For no particular reason, no two of the ones I have are the same. They were purchased at different times, and in most cases, from different stores.
Of the five, the only one that is 100% absolutely "bulletproof" with regard to RFI is an older 900 MHz unit labeled "AT&T" (and made by "who knows?"). It's off-white in color, and contains a digital voice recording-type answering machine in its base (no tape). Since I've had it for five years, I'm certain it is not a current model. No matter what band I use, or how much power, this particular unit receives no interference whatever, without my having had to add any filtering devices to it.
The others are branded SONY (2, but different models), and two are nondescript brands. It doesn't really matter, but all the other four cordless phones were BAD receptors of RFI until I add tons of filtering to them. In one case, I added an in-line filter having both inductors and capacitors, and in addition to that, it needed THREE clamp-on ferrite chokes in series, with the base unit telephone cord wrapped through each one three times (total of 9 turns!) to finally rid myself of interference, which for some reason peaked on 30 meters (maybe a resonant line length somewhere).
Moral of the story: When selecting a cordless phone, bring an RF-generating device with you, and get a demonstration of the telephone plugged into an active land line. Dial a local number, hold your handheld transmitter up against the base unit, and transmit to see what effect that has.
I've found that four out of my five phones would "fail" this test. The AT&T-branded unit, without modification, "passes" this same test. In my home experiment, I used a little Yaesu VX-150 5W 2m handie for the RF generator.
Based on the obvious correlation between RFI from a 2m source and RFI from HF sources, it appears a reasonably valid test.
The "failure" is obvious: In phones that are RFI-prone, the 2m handie signal causes a buzzing in the telephone headset. It cannot demodulate the FM signal, just the carrier alone causes the problem.
WB2WIK/6