|Why do I not always transmit a caller's phone number?
For privacy reasons, not the phone number for calls from the analogue network. Unless you explicitly allow Telekom submitting your number (free) and are switching to a digital office.
Who has an ISDN connection, it opposed the transfer of his number - or explicitly request that he on the transmission of his case by case number can decide (via ISDN; conditionally oppression [CLIR] is now free, conditionally Transmission costs extra). It drops the phone companies, however, seem very difficult, even in the first properly configured.
Who on the transmission of Caller Id is dependent, it should carefully check if everything is set correctly.