Can I use iPhone 4 micro sim in iPhone 3G?

a sim card is a sim card, if you get the contacts to connect to the card properly in the 3G, it should work fine. i gave my friend my old 3G (he had a first gen) and he swapped sim cards and it immediately worked.

I had a first gen that I gave to my friend after a water event, and she had to get a new SIM card for it. It took her a lot of wrangling to find the right person to talk to, but eventually it did work. This is on AT&T in the US. I bought the phone the first day it was available so it's possible that later ones changed something on the SIMs.

I did this with an old library card cut into the right shape for my adapter. Easy as pie, worked perfectly. I'm on AT & T too. I used the old sim for my template, then used my smaller card to figure out what to cut away.

As others have said, it'll work. You could also just walk into an AT&T store and ask for a SIM to fit your 3G. If you go that route, you can call AT&T to have them activate your iPhone 4 SIM when it comes back from the dead (fingers crossed).

On a side note, if you are within reasonable distance of an Apple store I HIGHLY reccomend taking your wet iPhone 4 in and having a genius check it over, wether it works after it dries or not. I've had experience with such things and generally Apple is more than fair about damaged phones.

Definitely try your hand at an apple store. There are multiple moisture sensors in the phone. My 3GS sat for about a day in a very shallow puddle of rain water that leaked inside the armrest of a car, triggering two of the five sensors. (I think that's what the genius told me). Here I sit tapping this on the replacement phone he gave me on the spot. First thing I tried was the rice treatment. After which my phone booted, but the home button was short circuited. The sensors visible from the headphone jack and the dock connector had turned red, but the tech opened the phone and those inside the phone didn't indicate water damage. So he said it was incidental damage, where if I'd dropped it in the sink or something I'd be on my own. I was also within my one year limited warranty. No AppleCare.