Hi Folks!
I have a iPhone 3G 16GB and I have the same tiny plastic crack between the earphone jack and the metal frame. I think that it is a bad mechanical design, maybe a not so enough strong polimer, or maybe the design is so thin. Anyway, I don't think that this can be solve exchanging the iPhone each time, because I will happen again. Moreover, I saw the the original iPhone headphones are more difficult (stronger) to plug/unplug in the jack, which makes more feasible the cracking. So, the only solution that I see too is a credit note or rebate from Apple for this issue.
What do you think? I paid 600€ for this new piece of hardware, I never suffered anything like this issue in my previous gadgets (MP3's, Mobile phones, etc.), and I think that Apple should do something to compesate us with this mistake.
Take it easy!