I'm still new at this, so I hope this is not a dumb question. I use Verizon here in the states (CDMA). I've bought a second, unlocked GSM phone to use in Europe. I'm going to buy local SIM cards there. It occurs to me that I might get a pre-paid SIM card here, with a small amount of minutes, so that I can use the phone right away for emergencies until I get the local SIM card.

Any suggestion on which carrier would be best to buy a US-based SIM card here on a pre-paid basis for this purpose?