The 2N2222 and 2N2222A comes in, and has always come in a metal can package. The manufacturers came out with an equivalent that was much cheaper because it does not have the metal package, it’s a regular TO-92 epoxy package. The 2N2222 and 2N2222A specifications require a metal can package, so the manufacturers named the plastic package PN2222A or MPS2222A. I seldom see experimenters using the correct number; for some reason they can’t simply read what it says on the transistor. Duh.
Oh, I’m sorry. I forgot. The bozos at a large chain of electronic stores didn’t want people to know this so they sold bargain packs of transistors with unknown numbers as “2N2222 Type” even though the packages were plastic, not metal. It was their fault, not the poor misguided consumer.
The picture shows the true 2N2222 used in a Joule Thief. As of Feb 2012, Mouser shows the 2N2222A costs $34.40 for a bag of 100, but the PN2222A is less than a quarter of the price, $7.90 a hundred (dollars U.S.). In quantity of 100, the discount is so great that you get four times the number of the PN transistors for less than twice the price, so it really pays to buy 100.