What is the lawful basis for using telephone data?

What is the lawful basis for using telephone data?

Telemarketing can be carried out using Legitimate Interest as the lawful basis of processing so long as the numbers are not used for automated cold calling (this requires consent). Considerations in any balancing test might include the time of day calls are made, an assessment of the vulnerability of the targets (possibly by the exclusion of certain age groups) and the frequency of calls.