My parents have two computers and an answering machine.  My brother bought
them the machine because he got tired of having to go over to their house
all the time.  For a while there, they were answering the phone in one part
of the house, then going to another part to pick up another phone.  The
first phone never got put back on the hook and they seemed never to hear the
obnoxious noise coming from it.  They refused to use the answering machine
at first, claiming they didn't need it.  Then one day, my brother simply
hooked it up for them and they were soon quickly amazed at the amount of
calls they were missing.

Then they went through a period of time when their phone just wasn't
ringing.  Again, we tried to tell them this, but they didn't believe us.
They could make calls, so they thought everything was fine.  They couldn't
explain why they were no longer getting calls.  They just thought that they
people they normally talked to were very busy. After several weeks, other
people began to complain to them, and they eventually realized there was
indeed a problem!

Eventually, the answering machine wore out and they replaced it with
voicemail.  This was a royal pain.  It didn't indicate whether or not there
were new calls.  And they rarely seemed to check it.  There were times I had
left 12 messages only to find out that they were home all the time and never
bothered to check it.  Another problem was that if there was one message on
there, the subsequent callers would get only one ring before the voice mail
would click on.  There were times when this happened when I was in their
house.  Sometimes they didn't hear that one ring at all.  Other times, my
Mom would say "Did you hear the phone ring?  I thought I did...  Oh, never
mind.  I must be hearing things!"  My brother and I both tried to convince
them that indeed there had been one ring and most likely there would be a
voice mail message.  But they never believed us.  Not even when we went to
the phone and played the message for them.  My Mom always replied "Now how
did THAT get on there?"

Worse yet, with this system, when they were online, you'd get a busy signal
when you called.  And with two computers, one or the other was seemingly
online all the time!  If it wasn't one of them, it was either my brother or
his teenaged son!

My brother eventually got them some kind of new setup.  Not sure exactly
what it is, but it makes the new voicemail (slightly better than the old
one) click in if they are online.  So you can leave a message.  But again,
it does not indicate to them that there are new messages, and I haven't been
able to impress upon them that if they have been online, it would be a good
idea to check it as soon as they get off.

Now, you'd think if they were online, you'd be able to contact them that
way.  But they don't check their e-mail very often, nor do they seem to
notice it when you instant message them on ICQ.  Actually, my Dad took the
ICQ off of his computer, blaming it for some sort of problem.  My Mom still
has it on hers.

So...  The best method of contacting them still seems to be physically going
to their house.  And if they're not there, leaving a message on their
kitchen table.  For some reason, they always seem to notice that.