JavaCard OS

Is there anybody working on sim cards? I am getting started with sim card.
Firstly, I want to write a simple java card program to run on sim cards. Can anyone point me some basic information on how to do this? How do I know what capabilities are supported by the sim card? How can I upload my program into sim card? Is operation the same as java card?

Just FYR
It seems to require one of these tools to upload your program to a sim card:
- GPShell from the GlobalPlatform project
- pyApdutool
- JCardManager

Kind note: It's pretty hard to get your code running on commercial mobile network operator SIM cards. They typically require the correct certificate before you can write to them.