"Children will give you a whole list. I had one give me three pages of an Excel file," he said, noting that the child even included the item numbers from the Toys 'R Us catalog for easier shopping. "Fifty items on each page."
"Then you have those that will go through the catalog and cut and paste the items into the letter," he said.
Recently, he got a letter from a 17-year-old in Japan reminding "Santa" that he didn't come when the letter-writer was 12.
"I was sad," the teen wrote. "So please try and visit my home this year. I will wait."
And all those volunteers -- those that can afford to -- are more than willing to go big.
On Friday, a woman picked up a letter from a child that only wanted a piano for Christmas, Fontana said, and she was determined to deliver.
"I said, 'Just one problem, a piano is not mail-able,'" he said. "So we wound up with a Yamaha keyboard."
After sharing this story on our broadcast and website, "World News with Diane Sawyer" received an overwhelming flood of e-mails with offers to help. Hundreds of people wrote, asking where they could send gifts to Santa letter authors.
"I was so touched to see the story about how different the letters to Santa are this year," wrote Linda from Middletown, Conn. "I just had my first child last December, and I feel so blessed that I can provide for her without a single thought. ... But so many parents are not as lucky."
Nicole from southern Louisiana wrote with several ideas for things to send.
"I would like to send a JC Penney gift card or a Wal-Mart gift card," she wrote, adding that she thought of purchasing a food voucher for a Christmas meal from a local grocer.
Dustin wrote us, "I'm 19 years old from Oxford, Ohio. ... I want to help as much as I can."
"We would like to help out the little girl who asked for a coat for her mom," wrote Arti. "This little girl isn't even asking for herself, and we want to help her."
Erika, a 25-year-old living in New York, saw our story and wrote, "It takes a moment like this to put the 'big' problems into perspective. ... Thank you for reminding us all what the holidays are really about -- giving, not getting."
And Dana, who's been out of work for two years, said he and his wife, Phyllis, were touched by the letters.
"Christmas will be somewhat light for us this year, yet we are still blessed and would like to share what we do have," he wrote.
ABC News has responded to each of these letter writers with information on how to help. If you want to help make a Christmas wish come true, the best way is by contacting a local post office participating in Operation Santa.
If there isn't a post office in your area taking part in the program, the U.S. Postal Service asks that you do an internet search in your area for other charities that also answer letters to Santa.