1) Pretty much any GSM phone on any GSM network. SIM cards are all the same. Some are larger capacity-wise than others, though. When the iPhone came out, there was some confusion about whether it contained some kind of special "3G" SIM, because people tried other SIMs in it and it didn't work. But there was nothing really special about the SIM, just the activation procedure.
You need a GSM network with EDGE data services to really be able to use the iPhone, though. In the US, that means AT&T and T-Mobile, as national providers, and perhaps some regional providers.
2) 99.99% No, not in any convenient or user friendly way.