i have nextel(which people who answer my questions should know) and i want an i phone 3G and i was wondering if i can put my sim in the 3G even if i jailbreak it and unlock it with Ziphone

No, you have to switch carriers. With the new iphone you have to activate at an apple store which takes about 15 minutes with someone who works at the store, and that means NO ziphone unlock. You also have to have a two year contract with at&t.

Sorry, you're outta' luck.