I am interested in the motorola olympus (that will have a tegra 2 processor), however, it is rumored that it will be released on the 4g network. I have absolutely no interest in spending an additional 120-180 dollars a year, so will it be possible to get a 4g device on a 3g plan, just not get the 4g service?
You are getting way ahead of things here! The Olympus, as I understand it , is GSM, so will not work on Verizon's network. Verizon doesn't have any 4G phones yet, and there's no pricing structure in place for 4G, or LTE, on Verizon at this point - it's all conjecture. Your question is meaningless at this point, and may be moot by the time Verizon does have 4G in place.
And as far as using a 4G device on the 3G network - the hardware is different - a 3G device will use the 3G network, a 4G device will use the 4G network, it's built into the device. (A very non-techy explanation) so I don't think it's possible to buy a 4G device and use it on a 3G network or plan, unless there is some sort of backwards compatibility built in as well.
Maybe someone who REALLY understands all this can step in and correct any errors I may have made and educate me at the same time!!
If it is a true LTE phone it will work on either AT&T or Verizon's 4G networks (that is my understanding), but of course you are correct SuzyQ, the OP could not then use it on Verizons 3G (CDMA) network.
All 4G devices should be backwards compatable and be able to be used on the 3G network. But if there is going to be a different price plan for 4G phones it's unlikely you will be able to opt out of it.
Grothka is correct, 4G devices will be backward compatible with 3G service. If this weren't the case, then Verizon would not be able to sell 4G devices to anybody that lived or travelled outside the 4G coverage area. Much like 3G devices can still utilize 1X networks when 3G is not available.