Hello,
Thank you for your question.
By stating "the simcard number" do you mean the GSM phone number your SIM card has?
There is no specific GPRS command to force device to send SIM card's GSM number.
You could set up device to send SMS to GSM number if event is generated by configuring an I/O element (For example Ignition - on change), then in GSM/SMS events section, enable your defined parameter to send SMS to a SMS Events PreDefined Number. After the I/O element status changes you will be informed with a text message in your phone and you will able to see the number.
As stated before device firmware does not have special command to request GSM number.
We hope it helps.
Regards.