There are two ways to do so:
1. 877 card
It works likes TurboSIM
2. SilverCard
You can program it yourself.
There is a full Tutorial to teach you how to do so.
http://www.weiphone.com/thread-4272-1-1.html
Please notice that all of them are made by Chinese iphone talents!
May need someone to translater into english.
And, as far as I know, this card is very cheap. (around 50USD only)
1. 877 card

It works likes TurboSIM
2. SilverCard
You can program it yourself.
There is a full Tutorial to teach you how to do so.
http://www.weiphone.com/thread-4272-1-1.html
Please notice that all of them are made by Chinese iphone talents!
May need someone to translater into english.
And, as far as I know, this card is very cheap. (around 50USD only)