If you have less than €1 of call credit, you can send a text message free of charge to ask your contact to call you back.
Type in the short code #111*Telephone number# on your mobile and press the call key. Instead of Telephone number, type in the number of your contact (without country code). Your contact will receive the following text message: Message from (your mobile number): "My call credit has been used up, call me back".
You can send this text message up to 10 times between two top-ups but only to national mobile phone numbers.
Discover all the other short codes to check your remaining credit, top up your Pay&Go card, activate bonuses, etc.