Deutsche Telekom and Vodafone switched off their service to send SMS from their landline telephone network to other landline phones or to mobile phones or vice-versa.
This happened at the 1st March 2023. Telekom said they informed their customers, but the German telecommunication news website "teltarif.de" cannot confirm this.
One of the users posted a comment where he asked the Telekom support and the support wasn't informed that the service had been discontinued.
To send a message, a special phone was needed. The phone then called a modem on 0193-010. That number is currently off-hook all the time.
If the recipient's phone wasn't capable of receiving SMS, a robot read the message aloud.
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O2 still operates their SMS gateway from mobile network to landline.