I just posted something about storytelling in the age of the iPhone - phone calls is one thing - but if everyone carries around the electronic equivalent of a deluxe Swiss Army knife - now that'll cause us to rethink, retool, retwist all sorts of things.

http://danielmartineckhart.blogspot.com/2011/02/screenwriting-in-iphone-world.html

How about McCauley (Robert De Niro) making a threat in Heat?

McCauley: Tell you what, forget the money.
Van Zant: What?
McCauley: Forget. The money.
Van Zant: It's a lot of money. What are you doing? What do you mean, "Forget the money?"
McCauley: What am I doing? I'm talking to an empty telephone.
Van Zant: I don't understand.
McCauley: 'Cause there is a dead man on the other end of this fuckin' line.

http://www.youtube.com/watch?v=lqNiYajjw5I

SWINGERS (1996) Mike leaves desperate messages on an answering machine.

[Nikki's machine picks up: Hi, this is Nikki. Leave a message]
Mike: Hi, uh, Nikki, this is Mike. I met you at the, um, at the Dresden tonight. I just called to say that I had a great time... and you should call me tomorrow, or in two days, whatever. Anyway, my number is 213-555-4679 -
[the machine beeps]
Mike: [Mike calls back, the machine picks up]
Mike: Hi, Nikki, this is Mike again. I just called cuz it sounded like your machine might've cut me off when I, before I finished leaving my number. Anyway, uh, and, y'know, and also, sorry to call so late, but you were still at the Dresden when I left so I knew I'd get your machine. Anyhow, uh, my number's 21 -
[the machine beeps]
Mike: [Mike calls back; the machine picks up again]
Mike: 213-555-4679. That's it. I just wanna leave my number. I didn't want you to think I was weird or desperate, or... we should just hang out and see where it goes cuz it's nice and, y'know, no expectations. Ok? Thanks a lot. Bye bye.
[hangs up]
Mike: [Mike walks away from the phone... then walks back and calls again; once again, the machine picks up]
Mike: I just got out of a 6-year relationship, Ok? That should help explain why I'm acting so weird. I just wanted you to know that. It's not you, it's me. I'm sorry... This is Mike.
[hangs up]
Mike: [Mike calls back, the machine picks up again]
Mike: Hi, Nikki, this is Mike. Could you just call me when you get in? I'm gonna be up for awhile and I'd just rather speak to you in person instead of trying to fit it all into -
[the machine beeps]
Mike: Fuck!
[Mike calls back, gets the machine again]
Mike: Uh, Nikki? Mike. It's uh, uh, it's just, uh, this just isn't working out. I think you're great, but maybe we should just take some time off from each other. It's not you, it's me. It's what I'm going through, alright? It's uh... it's only been 6 months ...
Nikki: [picks up] Mike?
Mike: [very cheerful] Nikki? Great! Did you just walk in or were you listening all along?
Nikki: Don't ever call me again.
[hangs up]
Mike: Wow. I guess you're home.

http://www.youtube.com/watch?v=vZChD_Gni8U

You gotta do the When Harry Met Sally 4-way phone conversation - when Harry calls his friend Jess & Sally calls Marie (Jess & Marie are in bed together) - a complete classic! But I can't find it on YouTube and it's not mentioned on IMDB.

Everyone talks about the phone call between Harry & Sally when they discuss Casablanca & he tells Sally she's High Maintenance - which is good, but to me the 4-way is a wonderful vignette.

The scene ends with Marie saying to Jess, "Tell me I'll never have to be out there again."

That's a good one from Heat.
And things left on a message machine could probably be a theme all to itself.
And that big back and forth in When Harry met Sally is perfect too.
I'll try and think of some others.

I like this tragic series of messages from Old School, they always make me laugh....

http://www.youtube.com/watch?v=He6Kcqy14HE

What about Jerry maguire?

[Rod has just told Jerry he will keep him as his agent]
Jerry Maguire: That's, that's great. I'm very... happy.
Rod Tidwell: Are you listenin'?
Jerry Maguire: Yes!
Rod Tidwell: That's what I'm gonna do for you: God bless you, Jerry. But this is what you gonna do for me. You listenin', Jerry?
Jerry Maguire: Yeah, what, what, what can I do for you, Rod? You just tell me what can I do for you?
Rod Tidwell: It's a very personal, a very important thing. Hell, it's a family motto. Are you ready, Jerry?
Jerry Maguire: I'm ready.
Rod Tidwell: I wanna make sure you're ready, brother. Here it is: Show me the money. Oh-ho-ho! SHOW! ME! THE! MONEY! A-ha-ha! Jerry, doesn't it make you feel good just to say that! Say it with me one time, Jerry.
Jerry Maguire: Show you the money.
Rod Tidwell: Oh, no, no. You can do better than that, Jerry! I want you to say it with you, with meaning, brother! Hey, I got Bob Sugar on the other line; I bet you he can say it!
Jerry Maguire: Yeah, yeah, no, no, no. Show you the money.
Rod Tidwell: No! Not show you! Show me the money!
Jerry Maguire: Show me the money!
Rod Tidwell: Yeah! Louder!
Jerry Maguire: Show me the money!
Rod Tidwell: Yes, but, brother, you got to yell that shit!
Jerry Maguire: Show me the money!
Rod Tidwell: I need to feel you, Jerry!
Jerry Maguire: Show me the money!
Rod Tidwell: Jerry, you got to yell!
Jerry Maguire: [screaming] Show me the money! Show me the money!
Rod Tidwell: Do you love this black man!
Jerry Maguire: I love the black man! Show me the money!
Rod Tidwell: I love black people.
Jerry Maguire: I love black people!
Rod Tidwell: Who's your motherfucker, Jerry?
Jerry Maguire: You're my motherfucker!
Rod Tidwell: Whatcha gonna do, Jerry?
Jerry Maguire: Show me the money!
Rod Tidwell: Unh! Congratulations, you're still my agent.