No one knows for sure. Here are some theories:
1) Ham, short for ham-fisted (i.e. can't send code for !@#$%^!!!)
2) Ham, short for Amateur
3) HAM was the callsign used in around 1908 before official ones were issued, for a station that was owned by three people whose last initials spelled out HAM (thus, the station's call...sorry, I don't recall the whole story)
Betcha a cold cheeseburger there are more, but none, so far as I know, is definitive.
--
Buddy Brannan, KB5ELV/3 | But I will lay my burden
Email: [log in to unmask] | in the cradle of your grace,
ICQ: 36621210 | And the shining beaches of your love,
http://www.ycardz.com | and the sea of your embrace.--Dave Carter