I would like to remind you that what I'm trying to discuss are the intrinsic differences of light, steady inflation, and light, steady deflation, of which I claim that there are NO economic differences (apart from the existence of a huge financial sector, but let us put that aside for a moment).  But I'm NOT discussing the effects of a TRANSITION from one regime to another.  I'm only considering steady, long term inflation versus steady, long term deflation.  In both cases, I assume that all economic actors in the examples are well-aware of this inflation or deflation, and adapt their previsions to it.

Because that's the question we want to answer: is (light) deflation *intrinsically* economically any different from (light) inflation ?  My statement is: no.  While a lot of common wisdom says yes. 

So I want to compare a deflationary monetary system to an inflationary monetary system, all else equal.

As such, if you say that during deflation, all prices fall, including wages, the mirror situation is that in inflation, all prices rise, including wages, of course.  And that people KNOW this.

So in as much as during inflation, I know perfectly well that if I earn $1000 today, I will earn $1020 next year, now, I know perfectly well that if I earn $1000 today, I will earn $980 next year.

So if I have to consider to buy a smartphone that costs me $500 today, or that will cost me $490 next year with my income of $980, or I have to consider to buy a smartphone that costs me $500 today, and that will cost me $510 next year with my income of $1020, what difference could that possibly make for me to decide to buy it now or next year ?

In both cases, I can choose between spending half of my salary on a smart phone today, or next year.

I consider the economic situation to be identical, so my risk to lose my job is the same in both cases.  My uncertainties are the same.
How could I be more inclined to buy now in one case, and to buy next year in the other case ?