what is 5.8GHz?

5.8GHz relates to cordless phones because it refers to the radio frequency the signals are transmitted on.

As far as are they worth the expense? It depends on your particular situation. Sometimes a 2.4GHz will work just fine. But if you ever may use a wireless computer network you are going to have issues since they will interfere with each other. In this case use 5.8GHz.

The phones shouldn't necessarily be that much more expensive, but they may have features you pay for (whether you care for them or not) that add to the expense (answering machine, better battery type, caller ID, extra handset, color screen).

Generally 5.8GHz is supposed to have more range and be clearer. I think this (range and clarity) was a bigger deal when people were switching from 900MHz phones to 2.4GHz. Personally if I didn't just use a cell phone anyway I would consider either, as long as I liked the phone and its features.

Its a very common phrase used mainly in computer studies...

means 5.8 Giga Hertz. In computer studies it says the spped of the processor.

In general Hertz is the unit used to measure frequency of anything. It can be a wave form it can be a motion of a partical... etc...

It's 5.8 GigaHertz. It's a frequency of the operation of the object.

I think it means

5.8*10^12 hertz

its the unit of freuency