Using an iPhone 3G as a backup to iPhone 4

[Pared]

Doing a bit of forward thinking here... and didn't see a thread on it.

I want to keep my 3G as a backup for whatever reason once I get my iPhone4. Problem is... 3G uses a sim card, 4 doesn't.

How would I go about swapping between the two? I can't have a sim AND micro-sim both hold my account information...right?

Is there such a thing as a micro-sim adapter?

 

[tersono]

Yes, there's an adapter. Your service provider should be able to let you have one.