Ok, I don't appreciate being told that I'm wrong by someone who's obviously too busy to supply the correct information, so here it is:

While RJ11 is the name of a specific wiring configuration on a registered jack, RJ12 and RJ45 are just common names for specific sized modular connectors. RJ12 is the 6 position modular connector.

Common wiring configurations on a "RJ12" jack are:

  • RJ11: one pair on the center two positions
  • RJ14: two pairs, one on the center two positions, and one straddling it on the next two out
  • RJ25: three pairs, two as in RJ14 and an additional pair on the outer two positions

Source: http://www.zytrax.net/support/ethernet/cables_jacks.htm and http://www.telepermit.co.nz/nl100.html#sec%203
Now that I've bothered to look, USOC has goodies, too.