I've been using StealthSIM SE with iPhone 3G for more than a month now, and I'm giving it up and got back to my iPhone 1rd generation.

Let me try to summarize my experience.

Voice, Data, SMS, even 3G works, no problem with the three major brazilian operators (TIM, Vivo & Claro).

But on all them I had constant "No Service" errors or "No SIM" errors. I had to reboot the iPhone 10 times a day to get the signal back. Some times I would only have voice service (no GPRS/EDGE/3G), usually a reboot would solve the problem.

I tried to stick a duck tape on the StealthSIM SE + SIM card to see if it would help, it got a little bit more stable but didn't have much improvement.

I also upgraded to, 2.0.1, 2.0.2 and now 2.1, same problems, so I'm giving up and will wait for a software unlock sollution.

My recommendation is to wait for the software unlock. Don't bother buying a SIM proxy that will need you to reboot your phone 10+ times a day or leave you with your sim tray stuck inside the iphone (I had to open my iphone once to get the sim out of the phone).

My $0.02.