Is it possible to use USSD queries, for instance to check the credit-level of my prepaid card ?
Yes, It’s possible to send USSD (Unstructured Supplementary Service Data) commands.
These messages are different from standard SMS messages, and such requests are usually not charged by the provider.
These messages can be sent using the SMS Component by using the “SendCommand” function of the Gsm object.
The trial version of the SMS Component also contains a number of samples which illustrate the use of USSD over GSM