Can I use my AT&T GoPhone Prepaid SIM in my iPhone 3G /3GS?

Sorry, No. It will not work. The iPhone cannot use a prepaid SIM or a pay as you go plan (GoPhone). The iPhone is activated with a pre-installed SIM. SIM-swapping can be done between iPhones in certain situations, but the iPhone is very SIM-specific. It doesn't act as a regular phone in the sense that popping in a different SIM will not work.

Yes you can. I have an old Samsung GoPhone that I activated just for this reason back in June. After activating the GoPhone, I swapped sims. I took out the real iPhone sim and replaced it with my GoPhone sim and the phone works great. The only thing is that anything requiring data won't work on an iPhone running 3.0 as 3.0 blocks data on sims running non approved iPhone plans.

The GoPhone sim will even activate the iPhone after doing a restore. This is true when using a 3G or 3G S iPhone. It will not work in a 2G iPhone. I have all three. Have fun!

"The only thing is that anything requiring data won't work on an iPhone running 3.0 as 3.0 blocks data on sims running non approved iPhone plans."

Isn't the only reason for having an iPhone its ability to deal with data and voice in such an amazing way (on 3G)?

It sounds to me like you've just confirmed that the 'Takers' have shot themselves in the foot! 😉

Well I still have my 3G S running it's own real iPhone sim. The GoPhone sim is now in the 3G iPhone. I don't care about using that phone with anything data related since I have my 3G S. I just want the extra phone number for certain calls. I can still use my WiFi connection at home to use data on the 3G.

3G still works with the GoPhone sim since the only thing required to use 3G service is a 3G phone.

I should also point out that the battery life on my 3G iPhone using the GoPhone sim is AMAZING! Since the data won't work, my battery will run a full week between charges.

"I should also point out that the battery life on my 3G iPhone using the GoPhone sim is AMAZING!"

Mine too on O2 in the UK with a VALID O2 SIM and with DATA!!!! I've not had less than four days since 3.0 and had NO problems with anything beforehand (AND we have tethering AND MMS already)!

Seriously, what HACKS ME OFF continuously is those who have problems of their own making because of their own 'taking'!

Live long and PROSPER (as they say in some parts)....people tend to GET just what they GIVE (we have found) 😉

Actually, the data WILL work on GoPhone if you want to use it. The 3.0 software changed the default APN settings. All you need to do is to change it back - you don't even need to jailbreak or unlock. Look here:

http://limitededitioniphone.com/iphone-os-3-0-7a341-kills-any-non-iphone-data-pl an-yeah-right-ive-got-you-covered/

Yes, I am aware of that site. I didn't think it was appropriate to post it here though.