You guys are jokers or morons.
The easiest, most casual thing to say is "Hey!"...Here I'll give you an example.
Me: "Hey!" [casual, not expecting anything out of the convo, just being cool, as if my friend just told me a funny joke]
Her: "umm, hi." [nervous probably, if she dont know u]
Me:
[if you semi-know her] "You know those shoes aren't in style anymore, right?"
[if you don't know her] "Is this Mr.DingDong's Math class?"
Her:
[if she semi-knows you] "haha, whats wrong with them?"
[if she doesn't know you] "Yeah(with a Why? intonation)"
Me:
[if i semi-know her] "Ohhh, nothing" say with a smile and like your keeping a secret from her.
[if i dont know her] "Haha, he's a crazy teacher, has he done <whatever> yet??" important to be friendly/easygoing/and humourous here.
Her:
[if i semi-know her] "You're mean" or something along those lines. There, you're in the door.
[if i dont know her] "Yeah, haha, he's <insert adjective>, do you like him?" There, you're in the door. If she doesn't keep the convo going with a question, ask her one next about the teacher/class. Then you're in the door. Make it brief and casual, leave her spinning.
Me: "Well, thats cool....I guess.....Say.......Wanna fvck?"
lol at that point its up to you, but thats generally how conversations go in the halls. No one's mean to eachother and at the worst will use you as social proof for her friends, it makes her seem more popular for randoms to talk to her.
Listen m8s, it doesn't matter what you say. The whole point of an "opener" is to get the message across that you're a fun guy to talk to and have a sense of humour. As soon as she laughs at a joke you make, or you pick up some IOIs(or whatever), get outta there, jobs done. Period.
Next time you see her, this is when you put your balls on the line. Ask her for her email or cell #, and tell her you guys should hang out some time. IMPORTANT: Don't ask her out, or put her on the spot, she doesn't know you well and will prolly be defensive. Just throw it out there that you think she's cool with an "We should hang out some time", nothing too specific, yet it gets the message across. Home phone is kinda weird in H.S. because parents and siblings use it too. Email or cell is more private.
Recap:
Step 1: "Hey"
Step 2: Be funny, find a detail about her that is humourous, and exploit it, at her expense.
Step 3: Go be busy somewhere else.
Step 4: Email / MSN / Cell