iPhone 2G can read some SIM cards, but not all? ("No SIM" message)

Hi,

Recently my iPhone 5 had to be sent in for a repair. And i dug out my old iPhone 2G(2007). To use in the meanwhile..

I've kept the SIM card i used with it back then(fullsize). And its been reading that just fine.

Then i wanted to use my NanoSIM from my iPhone 5(since thats where my plan is "planted" onto). And just a couple of days ago, it worked just fine(trying to test it). however, yesterday i shipped my iPhone to Apple. Tried putting the NanoSIM with a converter in the 2G and it wouldn't read it it gave the "No Sim Card installed" message.

My sisters IP5 will read the NanoSIM just fine. And the 2G will still read the old one.. And i can see that the 2G is actually touching the chip on the NanoSIM..(since its been worn down from being inserted 100 times..(still reads in my sisters iP5)

I've tried a thousand things. adding paper under the converter. rebooting. restoring in iTunes.. Nothing helps. That's why im here.

Can ANYONE help me? 🙂

the iPhone is running 3.1.3