Two new cordless phones from Uniden and VTech recently crossed a technological barrier -- they operate at a frequency of 5.8 gigahertz, up from the 2.4GHz and 900MHz used by older phones.

To judge from the numbers alone, that should be one giant leap for cordless-kind. More is better, right?

But under optimal conditions, manufacturers say, 5.8GHz phones have the same range -- half a mile -- as 2.4GHz phones.

Why so little difference? A cordless phone's maximum allowed strength ("maximum peak output power of the intentional radiator," as the Federal Communications Commission puts it) is 1 watt for most 2.4GHz and 5.8GHz phones. Some companies use less than that to extend battery life, so an 2.4GHz phone's range could be longer that that a 5.8GHz unit.

What's more, under city conditions, our roaming range -- half a block -- was no better with either of the two 5.8GHz phones than with an old 49MHz analog cordless phone. (The digital phones did sound much better, with brief drop-outs instead of the analog unit's maddening static.)

There is, however, one good reason to switch to 5.8GHz: Moving your cordless chatter to a less crowded chunk of the electromagnetic spectrum.

A 2.4GHz phone has to share that band with a lot of other gadgets -- wireless computer networks, microwave ovens, nursery monitors and others, said Stuart Lipoff, a partner with consulting firm Applied Value of Lexington, Mass., and past president of the IEEE Consumer Electronics Society, an engineers' association.

The 900MHz frequency of older phones is less crowded but still has plenty of traffic, such as medical devices, shoplifting tag systems and garage door openers.

Then again, the wide-open frontier of 5.8GHz can have limits of its own: A new, faster wireless-networking standard called 802.11a may intrude on that band in the next year or so.

The Uniden TRU5885 and VTech VT 5831 5.8GHz phones are attractive, full-featured cordless phones with indistinguishable reception. (The VTech handset actually transmits back to the base at "only" 2.4GHz, but we couldn't hear any difference.) Which one to get -- if any -- depends on your phone practices and preferences.

If, for instance, you get voice-mail service from the phone company, the VTech 5831 includes a set of flashing blue lights to notify you of new messages. Uniden's TRU5885 includes a built-in digital answering machine.

Each phone includes a speakerphone in its base unit. But the VTech's handset has its own stand-alone charger, allowing you to park it separately from the base unit.

You can add as many as five handsets to the VTech base unit and use an intercom to talk within the house. The Uniden allows two handsets and does not have an intercom.

Both handsets have Caller ID indicators and belt clips.

Both cost more than other cordless phones. VTech's model sells for $180, and each additional handset costs $80. Uniden's phone costs $169, with a second handset priced at $79 (the company's upcoming TRU5865, $149, has no answering machine.)

Meanwhile, there's a lot of life left in the older, cheaper bands. If wireless networking isn't in your future, a 2.4GHz phone should suffice; if you do use a WiFi network, a 900MHz phone may avoid interference just as well as a 5.8GHz model.

What .you do want to avoid is an analog cordless phone, since most do nothing to stop neighbors from listening in. "Anyone can get a scanner at RadioShack and listen to conversations on analog cordless phones," Lipoff said.

Digital phones, "spread spectrum" and otherwise, stop that kind of casual snooping, although they're not immune to a concerted effort from the likes of government agencies, Lipoff said.

Try all three kinds of digital cordless phones in a store. And since interference in your home may be worse than that in a shop, make sure you can return a model that doesn't work out.