I finally am able to get a pair of Etymotic ER-4S. I feel happy.
There's one thing that makes me curious though: How do I tell if my Ety is actually the ER-4S, not ER-4P or ER-4B? There doesn't seem to be any marking on the phones or the wire. There are two serial numbers, one on each phone, and they match the numbers on the white paper box, which is marked "ER-4S." But I am wondering if there is really no marking at all on the actual phones?