- Ackermann GmbH + Co KG
 - Bisenius Teleconsult
- Management and human resources consulting firm for the telecommunications and electronic media industries.
- Christoph Emmerich GmbH
- ISDN, PC-Karten, Telefone (in German).
- DETECON@
- Deutsche Telekom
- Provides public fixed-network voice telephony, mobile communications, text and data services, corporate networks, and on-line services.
- Ericsson Deutschland
- ExperTeach Gesellschaft fuer Netzwerkkompetenz mbH
- Praxisorientierte Schulungs- und Beratungsleistungen auf dem Gebiet der Telekommunikation
- lambda space GmbH
- Offers satellite components, systems, consulting, maintenance, and monitoring.
- RWE Telliance
- Telecommunications networks and services.
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