These are two but I believe related questions.

1.	Is an expandable phone network setup inherently vulnerable to interference?

I live in a large apartment on the second story of a vintage apartment
house in central Chicago. The walls are very thick and the building
has to have cable for residents to get even minimally good TV
reception because of interference from neighboring high rises. We have
2 phone lines, the second used only by the fax machine and my Mac
powerbook.

I wanted 4 cordless phones in the apartment, one of them with an
integrated answering machine. I wanted identical user interfaces so we
only have to memorize one set of instructions and settings.

I bought the well-reviewed Uniden TRU8885 cordless expandable phone
system (digital 5.8 Ghz) - a base and two extra handsets. I had
terrible reception and breakups from all the phones. The base unit was
the least vulnerable, but still inacceptable. I sent them back. They
replaced them with refurbished phones. After a few weeks I am having
the same problems again. I was very careful to charge the batteries
fully, etc. when I set them up.

I?m prepared to scrap them all, but reluctant to replace them until I
know what I need and what to avoid. I do have jacks in every room, and
I don?t need the 4-Way Conferencing  and 2-Way Radio Communication
features of the system. Would I be better off with 3 separate
identical cordless phones, each with its own jack but on the same
phone line?

2.	What about interference between different wireless networks? I also
want to install TIVO, which I understand is a network itself. I have
an AirPort Extreme base and want to set up a wireless network foor
laptop mobility on line. And I would like to use the X-10 technology
to turn on/off and dim lamps. (The priorities are as listed above)

So isn?t this potentially 4 network systems - the phone, the TIVO, the
AirPort, and the X-10?  Will I have problems with the remaining 3 even
if I omit the phone network?  I gather that a 5.8 Ghz network should
not interfere with the 2.4 AirPort network, but I?ve also seen that
disputed.

I?ve tried to educate myself online. I don?t trust anybody?s tech
support: it?s the kind of problem that each of the companies involved
wants to blame on the others, and and now I?m desperate!

I'm not sure about the 'phones
- once I had one and was interested to learn that the possibility of
using the same channel as a neighbour was quite high.

The Network thing is worth looking into, basically those things can be
encrypted or un-encrypted.
If they are open, then just about anyone can get into your WIFI LAN 
- a friend of mine (in a rural location) uses a local company's system for testing

quote: "I gather that a 5.8 Ghz network should
not interfere with the 2.4 AirPort network, but I?ve also seen that
disputed."

alla, where did you see that disputed? I would love to have a link to
that site because I am getting interference between my new uniden
5.8GHz phone (bought from Wal-Mart) & my 2.4GHz wireless network. When
I press the talk button on the phone, even my hardwired computers lose
network connection!

Thanks