I think you need to re-read what you read.
The home location of your phone on a GSM network either allows or denies you access to the network. If you phone's IMEI is not in a home location, you will NEVER BE ABLE TO CONNECT, regardless which GSM network you try to connect to.
What that does is tell the GSM phone providers who query for your IMEI number at your home location, whether a) you are a trusted device and b) whether we'll get paid to let you on their network or not!
The point of adding and removing is more of a refresh of authorization. The towers tend to cache certain authorizations and not accept new ones. Removing the authorization and readding it tends to clear it (don't blame AT&T, it's their damn vendor software doing this).
Sure I blame AT&T. When two parties enter into a contract they ONLY have legal obligation to each other in the contract. If I give the phone to my friend and my friend breaks my phone, I can't get out of my contract with AT&T because someone was acting on my behalf.... just like if AT&T has a contract with a vendor and they don't perform, my legal right is to go after AT&T as they're party to the contract with me, not the third party. Why do people have the mentality you have? I pay AT&T for a service, that as a professional organization they should be able to provide? What level is "reasonable" for dropped calls where they say I should have none? 10%? 20%? Maybe... The tech said my phone showed I dropped 61% of calls attempting to be placed.
To me, that's unacceptable.