Interesting topic!  Timelessness is difficult to achieve in any story where characters live and interact in a "real world" because of the plethera of items and events that we take for granted.  I suppose the more limited our life experience; the less we know about what we do not know.

I never gave your subject much thought until recently. 
Once was when my eldest sister's teen son encountered a rotary dial phone at a friend's beach house.  He did not know how to use it.  While growing up we never had one in our house but I had encountered the occasional rotary dial pay phone at school, Little League, etc.  Of course this was before ten year olds were all issued cell phones.
The other was when I was watching an old episode of "Batman" while babysitting some neices and nephews.  One of them wondered aloud as to why the opening credits included the phrase "In Color".  "Isn't it obvious that it's in color?"  She was shocked to learn that when "Batman" first came out the vast majority of American families had only one television in their homes and that it only showed black and white images.  Therefore, they would not know whether a program was broadcast in color or not.  She was relieved to hear that that monochromatic period in our history was actually before my time.
Finally, an example of historical perspective gone awry: Sen. Joe Biden recently opined that President Bush should do what President Franklin Roosevelt did during the economic crisis of 1929 and get on television to calm the people.  Of course there was no television in 1929 and Hoover, not Roosevelt, was President.  Sen. Biden was born in 1942.

Tschuss!
Hunter

I actually have a rotary phone in my house.  It's from about 1950 and rewired for a modular jack.  My little nephew thinks it's the craziest, most fascinating thing.  I only actually dial it a few times per year - I use my mobile for nearly all calls.

Let me tell you my situation: When I first published Satin Steele as a small-press Xerox-zine back in the early 1990's, my backstory for her had her as a high-school student (named Janet Steele) and gymnast, slated to be on the US Olympic women's gymnastics team going to the 1984 Games in LA.  (A tragic traffic accident on the way to the airport would inflict a broken leg on Janet, and take her father's life, preventing Janet's participation in the Olympics.)

Now that some 15 or so years have passed since those days, I'd have to update her "history" to make it the 2004 Summer games in Sydney, or something. 

Oops!    Thanks for the correction.