Question about iphone4 and simple mobile!!?

I just bought an iPhone 4 online, and it is version 5.1. I wanted to flash it to simple mobile. I took it to the simple mobile store, and they told me they can't flash it to their plan because mine does not have a SIMM card slot. That is how they put their service and data onto it. Apparently they told me they stopped making iPhones with sim cards for this reason. I have version 5.1 and they said only version 4.1 and 4.0 iPhone 4's have an SIMM card. Is there any other ideas? Anything helps? I looked online for the ones that I need and there is none. Any other plans or ideas? I already tried virginmobile and H20. Thanks!:)