If you have a house that can/will ship you boards registered between all layers at less than half a mil, and can finish solder mask suitably for .8 mm pin-pitch parts, let alone half mm, to .1 mil tolerances and coherent edges, and at competitive prices, then name 'em. Most of these houses won't even guarantee that they can etch to the tolerance that fine (.003") lines require without over/under etching.

My recent experience has taught me that no U.S. house will even attempt 'em even at 10x the "usual" cost. The reason, of course, is that it's difficult enough to get workers to show up and much less do their jobs, let alone put in the sort of concentrated effort that this sort of thing requires. That's especially true of holding thickness on the component side, lest the solder balls be too far from the surface.

RE