I still haven't tried it because i'm outside the US but check it out
http://www.youtube.com/watch?v=CWcGlfkkVM8
Post a comment if it works!
This is absolutely, 100% a scam. Or it will get you kicked off of Sprint/Verizon.
The SIM you get from Sprint/Verizon is a SIM from a partnership with an overseas GSM carrier. The only way you could conceivably use an iphone would be if you successfully unlocked it, but even then the SIM is set to the overseas carrier. You'd essentially be paying whatever roaming fees you pay for GSM to use it. And you'd STILL be getting AT&T's 3G even if you got it to work, since Sprint and Verizon don't maintain a GSM 3G network.
THIS WILL NOT GET YOU VERIZON OR SPRINT COVERAGE ON YOUR PHONE!!! IT IS PHYSICALLY IMPOSSIBLE TO MAKE A GSM PHONE COMPATIBLE WITH A CDMA NETWORK IN THE UNITED STATES!!!
Please don't hand these *******s your phone number. And anyone who does, do you mind posting what insanity they'll send you? I am curious to know what they're claiming to give you.