You are by now familiar with the saying There Aint No Such Thing As A Free Lunch (TANSTAAFL). Almost all offers on the Internet for free computers are hoaxes or identity theft scams. Obama may be giving away obamaphones, but they aren't smart phones, they are an expansion of a program begun under Clinton. Sorry, the best source for you is likely your public library, private charity, or a rescue mission. And considering your homeless condition, it's questionable if you need more possessions to lug around right now.
If you need a computer to do a job search, your local unemployment office (Dept. of Labor) offers free, & I believe, unlimited desktop computer use. (As well as resume writing help, typing tips, etc.) If you need a laptop to have or keep a job - agree, this can be very expensive, esp. right now. Suggest the same source - your local Dept of Labor office. They may be able to hook you up with a slightly older, used laptop at no cost, or help you purchase a new one for very low monthly payments. Start there. And good luck.