I believe that micropayments are viable between trusted points. By trusted, I mean that any surplus or debit between the two will be settled, on a daily/weekly/monthly/annual basis = no side will cheat the other. If cheating is possible, some form of escrow is needed, however, with escrow it is possible. The escrow must be a mutually trusted service.
I have a stock service and pay a fee to see a document or a quote, This is in milli$. 1000 M$ = $1. My monthly due is $2-3. They trust me and I settle, if over $1, once a month. Not settled rolls over to the next month. No escrow.
If I was doing an untrusted buy, I would have to involve an escrow service. My smallest buy is 1 milli$ - is a service that accepts and holds milli$ doable? It will be a simple accumulator/decrementer, but even so one side presents the document or stock quote to the escrow for a value of 1 milli$ who holds it until I pay the escrow the 1 milli$ and then serves it to me. On untrusted, there will not be a timely settlement period, as at all times the escrow MUST have either the 1 milli$ or the stock quote at all times and once mutuality occurs the escrow discharges to document to me and the 1 milli$ to the stock service. At the bottom end, say 1 milli$ the entropy of the exchange will have a value, which must be maintained or the escrow would suffer a heat death of $? - or the escrow could draw sustenance from somewhere - where is the question?