SIM: File structure.

Hi all, I'm making progress on the SIM/Filesystem applet. Data access commands are working, I'm now working on writing commands that send replies formatted as defined in TS 11.11 instead of FCI responses. I need input from you: I'm only a "smart card" guy, I can do "whatever is needed", but I need to define *what* is needed with you. I know especially nothing about GSM itself except that the MS talks with the SIM to manage cryptography, store SMS and phonebooks entries, etc. The SIM obviously relies on a filesystem. Some files are defined as mandatory in TS11.11, so I will include them, but their size is not always fixed. I'm opening this thread to define this kind of information. -what should be the N value for files whose size is defined by "3*N, N>=4"? -what optional files will be needed when the layer 2-3 will be ready to talk with the SIM? I let you read the TS11.11 spec to make your choice. Thanks, Sebastien