I'm only 19, but maybe you still want to hear my opinion..

I remember wanting a cell phone very badly when I was 12 as well, mostly because all of my friends had them, and I always saw them getting messages and I wanted that too.
My parents never got me one, because they said I could always find a public phone if I wanted to, and they didn't want to spend the money, and even if I payed for it, they didn't think i was old enough for the responsibility and they were afraid I'd get into debt, and all that stuff.

Of course I was furious, but after a while it stopped mattering to me so much, until I turned 17 and suddenly my parents urged me to get one, so I could call them in case I was out late and/or something happened!
Now the thing was *I* didn't want it any more, because I thought it was too expensive, and I didnt like phone calls anyway, and I knew that if you had a cellphone, people would never be on time, because they could always call you and tell you they'd be late.

after a while I gave in though and got a used one from a friend, which I still own, but never use. I hardly ever turn it on, even though I sometimes carry it with me when I go out. just in case.

So to make a long story short... I really don't think it would do your daughter any harm if you don't get her one, because even though she says all her friends have them (is that true? that's a lot for twelve year olds...), I'm sure they're not picking on her for it or anything.
It will just be something she can't get right away, something everyone has to go through all of their lives, and.. doesn't that build character? hehe no seriously, kudos to all the parents who can stand a little whining, and not have their kids turn out to be spoiled brats who always expect to get what they want.
She's really old enough to get over this, it won't cause any serious damage =)

the only reason why I'd give my child a cell phone would really be for when they leave for a few days or something, for emergencies. I live in germany and we use a lot of public transportation, and if you miss the last metro at midnight or something, you can call someone to pick you up.

so.. if you want to keep that option open, but still don't want to give her her own phone, have you ever thought about getting a family cell phone?
It would be there for "special occasions", and you could keep track of how much she's using it.

whatever you do, I hope it works out well for the both of you...

and by the way, I heard all the celebrities are getting rid of their cell phones, because nowadays that everybody has one, it has become a luxury to be unreachable