How patient should I be?

One suggestion, go back to using an old fashioned landline as us older folks grew up with landlines and don't need to think twice on how to use it..... just pick up the receiver and dial.

Also great to have landlines in case of an emergency at home, just dial 911 and the dispatcher will see on his/her screen your home address, so if the person calling is unable to speak due to a stroke or heart attack, EMT's can still be sent to the house quickly. Cellphones don't have the home address ability unless you order that option and pay for that service.... otherwise all dispatch sees is the nearest cell tower where the phone is pinging.

I have issues with my cellphone, too, hate it with a passion, but carry it only for emergencies and for simple texting. Cellphones have become just too complicated :P

As FF states, land lines are necessary for emergency calls. Even if someone was skilled with a cell phone, and even in a metropolitan area ilke I'm in, I still occasionally get "out of service" error messages. That's inexcusable in this day and age.

Landlines are more reliable.

To freqflyer and GardenArtist. Thanks for the answers. We have landline, with four phones in the house. He doesn't remember how to dial a number on them. We have the simplest flip phone (Tracfone), so don't know how to simplify any more.

I feel for both of you, having provided front line IT support for my parents (aaarrrggghhh - !) but then more recently been driven to physical violence by an iPod touch. Which just goes to show, I hope, that you don't have to have dementia to find current technology beyond infuriating.

Was he previously a big user of his cell phone? Will he miss it much if it gets discreetly "lost" or perhaps returned to the retailer for repairs, hem-hem?

Tell him the cell service is off line due to a glitch and put the phone away, hopefully he will soon forget about it.
Who is it he wants to call so desperately? You may be better off addressing that and helping him find other ways to communicate.
Older people have problems with modern phones, especially cell phones. You can't just pick up and answer, you have to push a button. Often the volume is set too low. Cell phone buttons are too small and it is difficult for clumsy fingers to hit the right ones. Add in cognitive decline and at some point they just become unusable.

I might just be temped to secretly remove the SIM card, try to turn on the phone and "discover" that it's not working, and conclude that likely was the problem he was encountering was the defective phone and not his inability to decipher the operating instructions.

Help him salvage his pride. And redirect his attention to something he can handle, or do something he enjoys - go out to dinner, play an easy board game if he likes them.... and let him know the phone is defective and that it's not his problem.

Try to keep him refocused on something he can operate and perhaps he'll forget about the phone. Tell him there was a recall on that model, something like that.

Your fathers obsession with the cellphone is his, not yours. Explain to your father how to use it, maybe a couple of times and then walk away and leave it with him. Ignore him and see if he can work it out, for your own sanity. You know he can't, but for yourself you need to stay back. Patience can not be measured in how trying a person can be, but in how you deal with an issue. All the best . Arlene Hutcheon