GDPR between two telecommunication companies

Answer:

It depends on the roles of the two telecommunication companies. If one of the telecom companies (company B) processes personal data on behalf of the other telecom company (company A) this means that company A is a data controller and company B is a data processor and in this case, there needs to be a legally binding document in place between the two companies. You can find a Controller to Processor Data Processing Agreement in our EU GDPR Documentation Toolkit (https://advisera.com/eugdpracademy/documentation/supplier-data-processing-agreement/).

You also need to have a legally binding document in place if the two companies are joint controllers as well.
Although not strictly required by the GDPR, it is a best practice to have GDPR Agreements also between two independent controllers.