Having a little “shredded tweet” for breakfast? 
That’s how I got my tiel. Just landed on me in the backyard. I think the little squatters are the advance guard of an alien invasion. 
Mine says quite a few different phrases including barking like the chihuahua. He whistles the Mayberry theme and I swear dances along with it. A lot of “tude” for a little bird.
We had a yellow cockatiel for several years. Ours would just perch on my book and chew the corners, wolf-whistle and crap. We had to find him an adoptive family when our new baby turned out to be allergic to the dander.
Our neighbor’s cockatiel was much more…interesting. We babysat him a couple of times when they went on vacation. He would wake us with, “Gimme a cracker, gimme a cracker!” Then, if the response wasn’t quick enough, “Fuck you,” with kind of a Southern drawl. The neighbors had 3 kids, so I always wondered a bit about that.
Mom’s cockatiel wolf whistles, calls the dogs (the dogs have been gone for several years), says “pretty bird” and “Lucy’s a pretty girl” annnnnd, most annoying of all… imitates the beepbeepbeepbeep of the microwave.
I did a short term contract on an IT campus in Austin, Texas. If I went outside in the afternoon I could hear what sounded like cell phone ring tones, pager beeps, and other electronic sound coming from the trees. It sounded exactly like the real thing, and I couldn’t figure it out. Someone I worked with clued me in: the trees were stuffed with mockingbirds, and most of them had picked up the various sounds. It’s really odd to walk past a tree and hear 3 different telephone rings coming from 10’ off the ground.
Note to self: do not teach Smalls any sounds. Like, ever.
Right now the only sounds I’ve heard have been the call-for-attention whistle, and a satisfied little chuffling sound when s/he’s riding around on a human.
That’s the injector going in.
Smalls will learn stuff like beepbeepbeepbeep on his/her own if s/he hears stuff like the sound of the microwave enough times. That’s how Lucy learned it.
hotflungwok how freaky and cool! 
Beadlin this site BirdsnWays helped me immensely when I was a new owner of a cockatiel rescue. The poor bird had been neglected and abused and was none too friendly. He was a confirmed seed eater and viewed anything I put into his cage other than seed as proof that I was trying to poison him. It took me six months to switch him to a pellet and fresh food diet. He came into my life when he was about six year old, and he lived with me another ten years. It didn’t take too long for him to fall in love with me and to tolerate the rest of the household, and he was an utterly fabulous companion bird. If you would like you may email me (addy is in my profile) and I will tell you how I went about changing his diet and a few other facts about life with a tiel. They really are a marvelous little bird, I have found them to be far more personable than budgies and not as much work as a larger parrot. They do have powder down which can be messy, and if they do not like a food item they are able to fling it through the bars of their cage an amazing distance, but once they fall in love with you, you are well and truly loved.
Birdsnways is a good starter site; I also recommend www.birdboard.com as a great discussion forum. They have extensive coverage on almost every bird topic you might think of and many more you wouldn’t. They really care about birds, and many of the regulars have upwards of 5, 6, or 7 birds!
'Tiels do that muttonchops thing when they’re feeling happy and relaxed.
Ok, since you might be keeping him:
VERY BAD THINGS:
Avocado, onion, chocolate. Don’t let him chew on anything galvanized/ zinc. Philodendrons and a whole pile of other innocuous houseplants.
Teflon, air-freshener stuff, epoxy, scented candles, oven cleaning, those metal pouch things some people cook turkeys in these days. Basically if it says “use with ventilation” don’t use it in the house within 2 rooms of the bird. Think canaries and coal mines.