I once worked at a Ford dealership. And the employee parking area had lots of GM and Chrysler brand cars parked in it.
When you’re hired by a company, they don’t force you to repurchase things you already own. Ford doesn’t require you to drive a Ford car to get the job.
The only employees who drove Fords at the time I worked there, were management who had employer supplied vehicles.
I have currently taken a position with a computer and printer company that is very high profile. And they have supplied me with their brand portable computer to use for work. But everything else I own is made by another company (simply because I already owned the other brand’s equipment prior to taking the position).
If a phone company intends their employees to only use their brand of phone, then they need to supply their employees with that phone, and pay the phone bill.
I currently continue using the phone I had prior to taking the position with my employer. And my employer even reimburses me triple my actual phone bill expenses. The company can issue me a company phone, but they’ll be required to provide it to me for free.
They also reimburse all of my transportation expenses. But if they want me to drive a certain car, then they also have to supply that car, and cover every expense for that car (maintenance, insurance, gas, etc.). Which they will do if I elect to take that option.
Any equipment mandated by the employer to be a specific brand and / or model, must be supplied by the company.