They can DESIGN a phone and make it so all the components fit but they don't "make" anything. The point wouldn't be moot as they have no clue what their doing..... they could keep every employee but they would still get crushed as any telecom they could buy would most likely have sub-par equipment and they'd have to spend millions/billions to make it competitive. PLUS there is that pesky tidbit of not knowing anything about the provider side of the business. Add on the fact that IF they were able to buy a telecom that means it was probably not doing well so why would you keep those know nothings on after they bought it?
Not sure why this is so hard in your mind.
Apple could buy Sprint and tell them to just keep doing their thing. (You know, other than giving iPhones special treatment.) But besides that Sprint sure as hell knows how to do all that other stuff.
Now, this is still a terrible idea because:
A) It's U.S. only. Apple would spend a lot of money to only cater to a portion of their audience.
B) Apple couldn't just shut down the rest of Sprint's business (without losing a ton of money) so they're now running a businesses they have no interest in.
C) Profit margins in this business are far lower than what Apple normally makes, so even in the part of Sprint that's doing "Apple stuff," they're not making nearly as much money as they're used to. It's just a big sink hole that takes wastes money and doesn't gain them much.
So, yeah, it is a terrible idea. But not for any of the reasons you've been posting.