Well, I tested on an iPod4...and what a disaster it was. Totally back to scratch.
I was just about to do my wife's iPhone 4 but realized a potential DISASTER.
Her iPhone4 on 4.2.1 is NOT a cell phone. It DOES have my iPad 3g simm in it. And, I changed something so that it can be used.
IF I upgrade her phone, and decide NOT to JB it (which is what I am thinking about doing), will I STILL be able to use the iPad simm in the phone? Or will the loss of the JB break the hack that I am using to make that work???
Previously, I used the iPhone4 and used MiFi occasionally, but I downgraded the plan on the iPad simm down to just the 250mb plan, and my wife does not use the MiFi, so I am thinking about NOT even JBing her phone. But, then it occurred to me that she will loose her 3g simm activation.