Are there phones that accept 2 SIM cards so a user can use 2 different cell phone providers if so does this include blackberrys?

At this current time there are no cell phones that are designed for the united states market that can accept 2 sim cards. I know that there are phones sold by Verizon wireless however that can use Verizon cdma network which doesn't require a sim card and then allow a sim for uses overseas on Vodafone's network. Besides that if you are really that set on having 2 sim cards in one phone then there are a few site that sell a piece which must be soldered onto the circuit board within the phone and then i have no idea how you can switch between the 2 sims.