My bet is that no provider except perhaps the best friend of you, would even try to aggregate ADSL via MLPPP. These are sold as individual products, period.

I can be wrong, let us know how it goes.

Note that once you configure NAT for all the four lines, and set four default routes to them, the lines will begin sharing the load very nicely, so aggregation is not need at all. Of course, the maximum speed for a single download, would remain the same as the individual line.

Actually, my buddy said they would never do it--too much of a headache to support. Yes, you will load balance the traffic. But, as you say, it is 4 individual links and not one link--a very distinct difference.