You have a sim-card and need to find what's you number. If your balance is active, you can call somebody, but if you can't do it? Of course, for different operators the commands are uniuque. But for AldiTalk there's such a ocmmand.

Go to the call interace, enter the number *#62# and press Call.
Attention! You need to call, and not to send a message or something else.
Then on the screan of your phone you can see your number.

There'e also another interesting USSD. It's not for a mobile operator, but for the phone with Android.
With the command '*#*#4636#*#*' you can check a lot. Уou can check which applications were used recently at the device. This will provide you with information about your phone, battery, Wi-Fi, and to use in General. But this command will not tell you the SIM number.