Firstly, do you know any ISC2 members who could endorse you after you pass the CISSP exam? If you do then maybe speak to them, explain your role in detail, and see if they can help you map your daily tasks to elements on the CISSP exam outline. If you can convince them you have the experience and they'll endorse you then that's all you need.
If you don't know any ISC2 members, you'd need to ask ISC2 to endorse you. This will involve giving details and documented evidence about your role (e.g. an offer letter from when you started the role). Given it's not clear cut even to you if your role covers the CISSP experience requirements as they are currently stated, it might be best to do a mapping of daily tasks to elements on the exam outline as part of your endorsement submission.
ISC2 keep their exams current through various workshops including one called the Job Task Analysis where they look at typical tasks security professionals undertake as part of their daily working activities. Through this process changes can be made to the domains of the certifications, including updates/removals/additions to the various tasks/subtasks within existing domains, or even updates/removals/additions of entire domains themselves.
As such, it is possible to argue that you are performing security functions as part of a role and therefore meet the experience requirement even if what you do isn't easily relatable to existing domains/tasks/subtasks. Although, obviously, it will be much easier to pass endorsement if your experience maps directly to existing domains/tasks/subtasks.
If you don't have enough experience you can always endorse as an Associate which will give you 6 years to gain the 4 years of experience you need. You can put the Associate designation on your resume (with some caveats) which along with your Sec+ might help you find a more security focused role.
In terms of your current role:
Are there ever any security considerations mentioned by your colleagues that need to be kept in mind while you're performing your usual duties? (I've worked with some mobile operators and security seems to be top of their minds.)
How about when you're working with the Linux environment, any security considerations while doing that?
At the very least I can't believe that everybody doesn't do this as part of their jobs, no mater what the role is:
Domain 1: Security and Risk Management
1.9 Understand and apply risk management concepts
-Identify threats and vulnerabilities
Do you follow secure working practices that apply controls so that if you make a mistake while optimising a cell tower you don't take it out of action?
Or when you're optimising your cell towers don't you need to make sure you don't turn the signal level up too high maybe due to emissions regulations?
Maybe that might fall under this:
Domain 1: Security and Risk Management
1.3 Determine compliance requirements
-Contractual, legal, industry standards, and regulatory requirements
I worked with a guy who absolutely met the CISSP experience requirements but for some reason he thought he didn't. He just needed some help in thinking about the daily tasks he used to do in a slightly different way and how they would then map to the CISSP domains. Sometimes we just don't appreciate all the facets of our roles at first. So just have a think about what you do and where security comes into it. Hopefully, that's all that's needed - a slight change in your viewpoint/mindset.
EDIT: Here are some links about AT&T's network reliability (aka "availability" the A in CIA) and network security to give you some insight into what they think is involved in operating their network securely:
https://about.att.com/csr/home/issue-brief-builder/people/network-reliability.html
https://about.att.com/csr/home/issue-brief-builder/people/network-security.html
