As a telecom security engineer, I’m assuming your main tasks will be of technical nature.
Considering that, ISO 27001 can help you understand the main concepts of information security and information security controls that can be applied to telecom, however, it will not provide you technical details on how to implement controls. For such knowledge, you should look for other certifications, like CISSP and CompTIA.
Regarding ISO 27001 certifications, if you want to consider an ISO 27001 career you can follow:
ISO 27001 Lead Implementer – this certification recognizes people who have competency in the ISO 27001 implementation process.
ISO 27001 Lead Auditor – this certification recognizes people who have competency in auditing an ISMS against ISO 27001 requirements and want to become certification auditors (and with this provides more confidence to an organization for being certified).
These articles will provide you a further explanation about ISO 27001 personnel certifications: