One of the Minecraft Classic lava and zombie survival servers I play on also has a SMP server, and why this should excite you is because they have a Mojang-hosted full Minecraft client (with some limitations, and I don’t think they will permanently be doing this) that allows you to play on their SMP server, although you can’t play on any other servers unless you have bought the game.
To play this, you will have to go to ablockz.org and make an account, which consists of your email, username (This should be exactly the same as your Minecraft account, because if you have a custom skin, it finds your skin by your Minecraft username) and password. You’ll then have to go to “Play Minecraft SMP” in the top right, and the server IP will be on the bottom of the page. Click Add Server and paste it into there. Once you’re in the server, you will have to set up a password by typing “/crazylogin password <password>”. Once you’ve done that, type “/login <whatever your password is>” and you’ll be un-stuck and ready to go.
I’ve been playing on here when I can waiting until I can get Minecraft, and then I’ll make a Killzone Helghast skin so I look like a boss.