This clue refers to the phone book.  If you look closely at the image, you will see there is a letter missing.  The letters go: I, J, K, M, N

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So the missing letter is 'L'

The text refers to two names that fit within the phonetic alphabet.  These are 'Oscar' and 'Charlie'

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So the answer is 'O' and 'C'

There are 2 pictures on the card that are of the same item but with a subtle difference - The fireplace picture found on the front and back page.  This is also referred to in the email from Charlie to 'check the fireplace'. If you look closely at the image on the back page, there is a letter K on the floor of the fireplace.

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So the letter is 'K'

If you look closely at the Teddy bear image, you will see that the bear's name is on his right foot: Ron.

The phone shows which letters correspond to which number.  So Ron equates to 7, 6, 6. 

Adding these numbers together gives you the total of 19.

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So the answer is '19'

This clue refers to the barcode on the back page of the card.

If you look closely at the numbers, there is one that stands out to the others.  The number 8

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So the answer is '8'

This refers to the time on the clock.  The time is 3:31.  If you add these together, you get 7

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So the answer is '7'