I think the bottom line here is...if you really want to save money.
if you have an grandfather plan...ride it as long as possible, because any current plans will not come any close in saving you money of you switch.
and for anything else.....is to treat your phone like its your baby so it can last as long as possible(weather if u got it on contract or non-contract, doesn't matter how it costs). the only real way to save money is to use a phone till it stops running on you (as long as it serves your needs)
but I know in reality different people have different needs. but I can assume 60% of us don't really have special needs. so don't go treating your phone like its a shoe. treat your phone like how to you treat a laptop (o wait, phones now adays cost as much as a laptop).
I don't know, that's my opinion.