The O2 SIM is a great deal for developers. It was first introduced to me by Kai Cherry. (Thanks, Kai!) You can buy a $10 SIM that lasts for 3 months (although it is advertised only for 1), with 5 cent SMS texts (10 cents for the first text of the day), approximately 14 cents per minute, and international calling that goes live within an hour or so after activation. You can also buy recharger cards at Big Lots or just keep switching to new SIMs if you don't care what number you're dealing with (Thank you, Google Voice!).
It's all great stuff. They're even adding data plans at the end of this Summer, according to customer support. No details are yet available but customers will be texted when the plan comes on-line.
Unfortunately, several of our readers had kittens when they saw that the screen shot said "O2" instead of "AT&T." So this morning, I got my hands on a standard, branded AT&T iPhone SIM and re-did the tests using that SIM instead of the O2 one. Results? The same. The 3GS (the leftmost of the two phones shown above) continued to have better signal strength, both raw and graded, as shown in the screen shot above. You can see the O2 SIM in the picture, just to the left of my 3GS.
Other readers asked that we do a side-by-side kung-fu-grip-of-doom-head-to-head. The two side-by-side pictures included in the gallery below the results. In order to mano-a-mano that deathgrip, one of the phones needed to be upside down in my right hand. To keep things fair, I did the shot twice -- once with the 4 upside down, once with the 3GS. As you can see, once again, the 3GS prevailed. It consistently maintained a functional signal strength despite kung fu gripification. It also taught me exactly how hard it is to hold two phones at once while taking a snap shot on a third -- had to use a stand and my nose.
So there you have it. Any more questions or concerns? Let us know in the comments.