Switching carriers

That would depend who owns the account. If he owns it he would have to allow you to switch or he could switch it for you via doing nothing and letting you switch carriers.

Unfortunately if he owns the account no one can just switch carriers. 
in my family I have my wife have a sub account that is part of the whole. She has administrative rights to change and or port out if she wants.

the other issue is some accounts have bonuses and discounts that would impact one or more accounts to leave. 

on our accounts we have veterans discounts and credit card use of payment as well as our apple watches are sync with our iPhones and of course the discounts depend on three lines of service not including the watches.

so lot to think of. 

Unfortunately if he owns the account no one can just switch carriers. 

@elector That is not true. The only information required to port a number is the account number and account pin. Obviously, if the OP doesn’t have that information, the account owner would have to provide it but no other permission from the account owner is needed. If the OP has the account number and account pin, any carrier will port the number.

Cellular carriers as well as home phone owners cannot just switch a service with out checking with the owner of the account.

Any cellular carrier that would not take precautions with their customers would open themselves for (Edited per community guidelines), state and federal complaints.

Lets just say for giggles here someone should find or grep your phone information. You then find your account highjacked (and yes this has been done just google it) or crammed I think it is also referred to.

If say my wife wants to switch to any carrier from our verizon service, she would not be able to port out unless I gave permission and allowed her to port out. That is why the account number and PIN are needed. In fact our account has two pins. 

But in no way any account owner would simply allow the secondary phone to be switched out. As I said in my last reply. Causes too much issues. 

Now some carriers will allow a person to assume responsibility (assumption of Liability) for the number with credit approval. That is a different issue as well.