Could it be that the Crematorium had 'broken down' and failed to tell its customers.
This is what I think happened.
Deciding to bury this lady in the back garden instead, Harry the Cremator now turned grave digger had the task of opening the casket, after all it was much easier to bury a body than a whole casket with a body. He could sell this casket off to George the local undertaker who 'knew' of his little 'problem' with the furnace.
Opening the casket he found Mrs Mac Donald dressed nicely in her best blue suit and lo and behold she was clutching a cell phone in her dead, white, little fingers. Harry's eyes gleamed with the pleasure of unexpected profit and he removed the phone from Mrs Mac Donald's grasp. Nice little clam style Motorola. This would go nicely on ebay! Or he could even keep it himself as a surprise gift!
He hauled the stiff body of Mrs Mac Donald out of the casket and placed her in the wheel barrow that he had prepared. Quietly he wheeled the body out to the back yard to the pre dug grave, unceremoniously threw it into the hole and then refilled the hole.
Suddenly a wicked thought crossed his mind. He took the cell phone out of his pocket and switched it on. The battery was well charged and there was credit on the phone. He checked through the address book. Jim, Karen, Alice and Paul were the listed names. Harry smiled wickedly! Well, it was just a little fun! After all he was doing them a favour disposing of their mother for them, he deserved a little extra pay back. Quickly, Harry rang each of the names three times and then hung up. He smiled to himself again! Think what a story they could tell their grandchildren! Yes, he was definitely adding a little fun to everyone's life with this.
As for the phone, that was easy. He would simply remove the old SIM Card, pop in another one and 'Bob's Your Uncle' he'd keep this phone for himself!
Feeling contented with his day's work Harry returned to the crematorium to await his next customer! He wondered what surprises he would find in the next casket.